Mr. Justice Clark
delivered the opinion of the Court.
These consolidated cases involve claims of United Air Lines (United) and the Association for the Benefit of Non-Contract Employees of United (the Association), attacking the form of ballot that the Board intends to use in a representation election among United’s employees under § 2, Ninth» of the Railway Labor Act, 44 Stat. 577, [653]*653as amended, 45 U. S. C. § 152, Ninth (1958 ed.).1 United also contends that the National Mediation Board (Board) should hold a hearing under the same section, with its participation, to determine the appropriate craft or class in which the election should be held. Before the Board the conflicting unions — Brotherhood of Railway and Steamship Clerks (Brotherhood) and International Association of Machinists (Machinists) — agreed that the appropriate craft or class in which the election should be held was “clerical, office, stores, fleet and passenger service employees” ; over the objection of United the Board ordered an election in this unit to determine which union, if either, would be its bargaining representative. United then filed suit against the Board raising the questions it presses here. This case was dismissed and is here, after affirmance by [654]*654the Court of Appeals, as No. 139. After this dismissal the Association filed suit against the Board, the Brotherhood being permitted to intervene, and raised substantially the same claims. The District Court enjoined the Board from conducting an election with a ballot that did not permit an employee to cast a vote against collective bargaining representation; the other issues were remanded to the Board for further consideration. 218 F. Supp. 114. The Court of Appeals affirmed these cases by a divided court and they are here as Nos. 138 and 369. 117 U. S. App. D. C. 387, 330 F. 2d 853. Judge Wright, dissenting, thought the District Court was without jurisdiction to enjoin the Board from conducting a representation election, citing Switchmen’s Union v. National Mediation Board, 320 U. S. 297 (1943). We granted certiorari in all three of the cases. 379 U. S. 814.
We hold that the Board satisfied its statutory duty to investigate the dispute; that United is not entitled to be a party to proceedings by which the Board determines the scope of the appropriate craft or class; and that the Board’s choice of ballot for its future elections does not exceed its statutory authority and is therefore not open to judicial review.
1. The Facts.
In January 1947, after lengthy hearings in which United and other airlines participated at the request of the Board, it was determined that the “clerical, office, stores, fleet and passenger service” grouping of employees constituted an appropriate craft or class, within the meaning of the Act, for collective bargaining purposes. Case No. R-1706, N. M. B. Determinations of Craft or Class 423 (1948). All of the parties here, save the Association, participated in this public hearing. Since that time they have participated in other cases involving the same questions decided in R-1706, but, with some exceptions, the [655]*655Board has continued through the years to hold elections in that craft or class.
In August 1962 the Brotherhood filed with the Board an application under § 2, Ninth to investigate a representation dispute among employees of United. In its original application the Brotherhood proposed to exclude those stores and fleet service personnel then represented by the Machinists. After the Board had advised United and the Machinists of the Brotherhood’s application each informed the Board that in its opinion the application should be dismissed because it did not conform to what the Board had found to constitute a craft or class in Case No. R-1706, supra. Alternatively, United requested that if dismissal was not in order the Board should hold hearings to determine the proper craft or class in which the election should be held. Upon receiving notice of this opposition the Brotherhood amended its application to include the full craft or class approved in R-1706. The Machinists then agreed that this was the appropriate unit in which to conduct the election.
The Board concluded that a dispute existed requiring an election and scheduled one for January 1963. It proposed to use its standard form of ballot which provided for the printing of the names of the labor organizations— in this case, the Brotherhood and the Machinists — with a box below each name for the employee to check the representative preferred. A third space was provided in which the employee could write in the name of any other organization or individual he wished to represent him. There was not a place on the ballot in which the employee could vote specifically for “no union.”
The Board, on December 19, 1962, directed that a list of the employees involved be supplied by United not later than January 14, 1963. On January 11 United advised that the request was premature and requested a hearing as to the scope of the unit involved in the Brotherhood’s [656]*656amended application. It outlined in some detail the past practices of the Board in dealing with such requests and attacked the continued suitability of the R-1706 determination, asking that the case be re-opened and that the group be divided into three separate crafts or classes. On January 17 the Board denied this request. It pointed out that United on September 7, 1962, had objected to the craft proposed in the Brotherhood’s original application on the sole ground that it did not conform to R-1706; that the Brotherhood had then amended its request to conform with R-1706; that United had been notified of this change on October 8, 1962; that on October 24 the Board had requested United to furnish the number of employees in the craft or class as amended and that it had furnished this information on November 2, stating that there were 12,451 as of a given date; and that it had failed to furnish the names of the employees. The Board then commented that “the carrier is not a party to this representation dispute”; that “no request for a review of... Case No. R-1706, et al. has been received from either organization party to NMB Case No. 3590” (the pending application of the Brotherhood); and that United’s request was “not timely made, since the Board, on December 19, 1962, found that a representation dispute existed among the employees in this craft or class, and has authorized an election.” United requested reconsideration of this decision, but without success.
Meanwhile, on January 18, 1963, when United advised the Board that it was “willing to allow a ballot box election on Company property provided the ballot follows the form used by the National Labor Relations Board,” i. e., the ballot “would have a space for the employee to vote against representation as well as space for the employee to vote for representation” by the Brotherhood or the Machinists. (Emphasis in the original.) The Board replied that its form of ballot had been used since 1934 [657]*657and that it saw no reason to depart from it. Thereafter United advised that it would furnish the list of employees by February 11, but on that date the list was refused and action was begun the next day against the Board in the District Court for the District of Columbia. This case was later dismissed, as we have noted.
It appears that while the election was being delayed the Association was being organized among United’s employees. By March 1963 it claimed 6,400 members, about 50% of the total number of United’s employees. It sought, like United, to be heard in a craft or class proceeding and to have the ballot amended. It stated, however, that it did not seek recognition as a bargaining representative, and it did not want its name on the ballot. It intended to dissolve after the election. The Board denied the applications.
After United’s case was dismissed, the Association filed a similar suit in the same court, seeking substantially the same relief. The Brotherhood was permitted to intervene, and it filed a separate appeal from that of the Board after the court had disposed of the case as we have already stated.
After we granted certiorari, the Board adopted an amended form of ballot on which there appears the following directly above the names of the unions seeking election as representative:
“INSTRUCTIONS FOR VOTING
“No employee is required to vote. If less than a majority of the employees cast valid ballots, no representative will be certified.”
In effect, this amended ballot stated on its face what has been the practice of the Board in these elections since its inception. The Board has announced its intention to use this form of ballot in future representation elections, including any that may be held in this particular matter.
[658]*6582. The Purposes of the Act and the Board’s Function.
The major objective of the Railway Labor Act, 44 Stat. 577, as amended, 45 U. S. C. §§ 151-188 (1958 ed.), was “the avoidance of industrial strife, by conference between the authorized representatives of employer and employee.” Virginian R. Co. v. System Federation No. 40, 300 U. S. 515, 547 (1937). Section 2, Ninth set up the machinery for the selection of the representatives of employees. It authorized the National Mediation Board, upon request, to investigate disputes over representation; to “designate” those who were affected; to use a secret ballot or any other appropriate means of ascertaining the choice of employees; to establish rules governing elections and to certify the representatives so chosen to represent the employees in negotiations. Upon the issuance of this certificate the employer, under the Act, is required to “treat” with the representative certified to it by the Board. As we said in Virginian R. Co.: “The statute does not undertake to compel agreement between the employer and employees, but it does command those preliminary steps without which no agreement can be reached. It at least requires the employer to meet and confer with the authorized representative of its employees, to listen to their complaints, to make reasonable effort to compose differences — in short, to enter into a negotiation for the settlement of labor disputes such as is contemplated by § 2, First.” Id., at 548.
In Switchmen’s Union v. National Mediation Board, 320 U. S. 297 (1943), the petitioner sued for the cancellation of a Board representation certificate. The Court held that the Act precluded review of the Board’s certification of a collective bargaining representative under § 2, Ninth. The case involved a question of statutory con[659]*659struction, i. e., whether the Act permitted the division of crafts or classes of a single carrier into smaller units for collective bargaining purposes. The Court refused to consider the merits of the claim, holding that it was for the Board, not the courts, finally to resolve such questions. “The Act in § 2, Fourth,” the Court said, “writes into law the 'right’ of the 'majority of any craft or class of employees’ to 'determine who shall be the representative of the craft or class for the purposes of this Act.’ That 'right’ is protected by § 2, Ninth which gives the Mediation Board the power to resolve controversies concerning it and as an incident thereto to determine what is the appropriate craft or class in which the election should be held.” Id., at 300-301. The Court goes on to note that Congress decided on the method which might be employed to protect this “right”; and that where Congress “has not expressly authorized judicial review,” id., at 301, “this Court has often refused to furnish one even where questions of law might be involved,” id., at 303. The Court’s conclusion was that “the intent seems plain — the dispute was to reach its last terminal point when the administrative finding was made. There was to be no dragging out of the controversy into other tribunals of law.” Id., at 305. Thus, the Court held there could be no judicial review.
It is sometimes said that in Leedom v. Kyne, 358 U. S. 184 (1958), the Court created an “exception” to the doctrine of Switchmen’s Union. In Kyne, it was held that the law afforded a remedy in the courts when unlawful action by the National Labor Relations Board inflicted injury on one of the parties to a bargaining dispute. But this was no exception to Switchmen’s Union. Rather the Court was careful to note that “[t]his suit is not one to ‘review,’ in the sense of that term as used in the Act, a decision of the Board made within its jurisdiction. Rather it is one to strike down an order of the Board [660]*660made in excess of its delegated powers and contrary to a specific prohibition in the Act.” Leedom v. Kyne, 358 U. S. 184, 188. (Emphasis supplied.) The limited nature of this holding was re-emphasized only last Term where we referred to the “narrow limits” and “painstakingly delineated procedural boundaries of Kyne.” Boire v. Greyhound Corp., 376 U. S. 473, 481 (1964). It is with these principles in mind that we turn to the questions in the instant cases.
3. The Craft or Class Determination.
The order of the1 District Court in Nos. 138 and 369 enjoins the Board from conducting an election “in which the form of the ballot does not permit a voting employee to cast a vote against collective bargaining representation . . . .” The Association concedes that the order does not enjoin the holding of the election until the Board reconsiders its craft or class determination; nor has it petitioned here for a review of that portion of the decision.' Thus, we need not reach the question of the Association’s right to demand or participate in proceedings leading to such a determination.
The same is not true of United, however, for it specifically sought and was denied such relief, and it comes here contending that this denial constituted error. United argues that since the Act compels it to treat with the representative chosen by the majority of its employees in the craft or class in which the election is held, it has a direct and substantial interest in the scope of that unit; and that since the Act provides for no administrative or judicial review, due process requires that it be accorded an opportunity to participate in the proceedings by which the Board determines which employees may participate.
It also contends that the Board, in designating the employees who could participate in the election, did not do so as a result of the statutorily required investigation— [661]*661which, United contends, requires that the Board take evidence and make findings — but made an arbitrary determination, relying solely on the agreement of the unions.
United’s position is that Switchmen’s Union does not control a claim that the Board has ignored an express command of the Act. This particular question was reserved in the 1943 cases. In General Committee v. Missouri-Kansas-Texas R. Co., 320 U. S. 323 (1943), a companion case to Switchmen’s Union, the Court stated: “Whether judicial power may ever be exerted to require the Mediation Board to exercise the 'duty’ imposed upon it under § 2, Ninth and, if so, the type or types of situations in which it may be invoked present questions not involved here.” Id,., at 336, n. 12. We think that the Board’s action here is reviewable only to the extent that it bears on the question of whether it performed its statutory duty to “investigate” the dispute.2 Reviewing that action, however, we conclude that the contention is completely devoid of merit.
Section 2, Ninth makes it the duty of the Board to “investigate” a representation dispute and “to certify to both parties, in writing, within thirty days after the receipt of the invocation of its services, the name or names [662]*662of the individuals or organizations that have been designated and authorized to represent the employees involved in the dispute, and certify the same to the carrier.” This command is broad and sweeping. We should note at the outset that the Board’s duty to investigate is a duty to make such investigation as the nature of the case requires.3 An investigation is “essentially informal, not adversary” ; it is “not required to take any particular form.” Inland Empire District Council v. Millis, 325 U. S. 697, 706 (1945). These principles are particularly apt here where Congress has simply told the Board to investigate and has left to it the task of selecting the methods and procedures which it should employ in each case.
In dealing with the sufficiency of the investigation it is necessary to examine the experience of the Board through the years in resolving questions of craft or class appropriateness. That experience, insofar as it concerns the unit involved here, dates back to 1946 in Case No. R-1706, supra, when it was called upon for the first time to apply the craft or class principle of representation to the airline industry. At that time it had before it a fledgling industry, a relatively new statutory command and a huge group of employees for whom there were no recognized crafts or classes within the meaning of the Act. At least five unions were involved, all urging different employee groupings, and all of the major airlines were invited to participate in an extended public hearing. United was among those participating and in fact supported the very craft or class unit which the Board eventually decided upon and to which it has adhered here. Because it was the first time the Board had recognized such a craft or class, it cautiously provided in denying reconsideration of its determination that it was subject [663]*663to future re-examination where to do so would further the purposes of the Act.
Thereafter began a period in which the workability of the R-1706 determination was tested in practice, and it did not go completely unchallenged. In 1948 United voluntarily recognized the Machinists as the collective bargaining representative for its ramp and stores employees. It supplied the Board with evidence upon which this recognition was based and its reasons for departing from its usual policy. It is noteworthy that the Board replied that voluntary recognition would not preclude future determination by the Board of the proper craft or class to which those employees would belong. In 1951 the determination of R-1706 withstood challenge in Matter of Representation of Employees of Northwest Airlines, Inc., Case No. R-2357, 2 N. M. B. Determinations of Craft or Class 60 (1955). United submitted a statement in this proceeding, emphasizing its disagreement with the R-1706 decision and requesting that it be disregarded. The Board refused to do so, but it did reiterate what it had implied in 1947 — that it was “of the opinion that upon proper application ... it will be advisable to reexamine the determination in case R-J.706 et al., with the view of making such modifications as may be found to be justified at that time.” Id., at 67. We note that in both cases — R-1706 and R-2357 — the unions competing for representative status were in disagreement as to the appropriate unit in which elections should be held. Again in 1952, in Case No. R-2482, 2 N. M. B. Determinations of Craft or Class 72 (1955), United participated when the Air Line Dispatch Clerks Association sought to represent its general dispatch clerks, dispatch clerks A, B, and C and crew schedulers; the Brotherhood there disputed the grouping, contending that R-1706 established the scope of the election. The Board sustained this position, which was also that of [664]*664United, and held that R-1706 should be adhered to. United had argued that the dispatch clerks and schedulers were not a separate craft or class but merely components of the R-1706 unit, and that representation could be had only through investigation and election in that group. The Board ultimately discussed the application in these terms:
“The precedents heretofore established by the Board, however, cannot be disregarded. Moreover, the record of stable industrial relations which has followed in the years since the Determination in R-1706 must be given due and careful consideration.
“. . . In an industry which is still expanding, the agency charged with the duty of certifying designated representatives for collective bargaining must of necessity hesitate before acquiescing In the desires of certain employees to establish small segregated groups, because by that very course it may retard, or even destroy job opportunities. Flexibility in the use of employee talent carries just as many advantages for the employees as it does for the carrier. The Board is fully aware that the action taken herein will have, as an end result, the withholding of an immediate opportunity to select a collective-bargaining agent by this group of employees, but nevertheless, it is convinced that the basic purposes of the Railway Labor Act will be better served by adherence to the policy of preserving established crafts or classes.” Id,., at 76.
Nor do the subsequent cases brought to our attention strip the R-1706 decision of its continuing validity. In both these matters — Cases No. C-2252 and C-2389, 3 N. M. B. Determinations of Craft or Class 16 (1961) — the Board determined that stock and storeroom employees were separate crafts or classes of employees at North Central and Trans-Texas Air Lines. Neither of these airlines [665]*665had participated in the 1946 proceedings. Both were feeder lines, and in both cases the contending unions disagreed as to the appropriate unit in which the election should be held. In any event, the Board was simply pursuing the policy it had announced when it decided R-1706 — that it would re-examine craft or class determinations when it thought the purpose of the Act would be furthered thereby. This in itself belies the notion that the Board has blindly followed the R-1706 ruling.4
It is in light of this background that we must decide whether the Board’s reaffirmation of the R-1706 determination in these cases was made after a sufficient investigation, within the meaning of the Act. We reject the contention that it adhered solely to the craft or class chosen by the unions. Time and again it has acknowledged that it has the task of determining the appropriateness of a craft or class, and nothing in this case suggests that it abdicated that responsibility here. Where units untested by actual collective bargaining have been proposed by the unions involved the Board has consistently held hearings to determine the propriety of holding elections in those crafts or classes. But where the unions have agreed and the unit they have agreed upon has been one well-established in industry bargaining circles, it has. usually held elections without full-scale hearings, not simply because the unions agree but because the unit upon which they agree is one that is well-recognized under prior determinations of the Board and has proven satisfactory in actual experience. This is what it did here.
[666]*666The Board received the Brotherhood’s application; it requested, received and considered statements from the carrier and the Machinists. On the basis of these preliminary actions, it scheduled an election. But it continued to correspond with United, accepting and studying its detailed application for reconsideration of the Board’s decision to proceed to election in the R-1706 craft or class. Viewed alongside prior experience with the R-1706 grouping in the air transport industry this procedure clearly complied with the statutory command that the Board “investigate” the dispute. The only missing element of the required investigation is the election and that can now be held promptly.
United sought to have the District Court require the Board to hold a hearing on the craft or class issue in which it would participate as a “party in interest.” But the Act does not require a hearing when the Board itself designates those who may participate in the election. It provides that “the Board shall designate who may participate in the election ... , or may appoint a committee of three neutral persons who after hearing shall within ten days designate the employees who may participate in the election.” (Emphasis supplied.) Indeed, United seems aware of this, for it stated in its brief that if “the Railway Labor Act does not specifically require a hearing, it does require an ‘investigation,’ ” and that United must be heard in the course of that proceeding. Clearly, then, the Board cannot be required to hold a hearing.
Nor does the Act require that United be made a party to whatever procedure the Board uses to define the scope of the electorate. This status is accorded only to those organizations and individuals who seek to represent the employees, for it is the employees’ representative that is to be chosen, not the carriers’. Whether and to what extent carriers will be permitted to present their views on [667]*667craft or class questions is a matter that the Act leaves solely in the discretion of the Board.
The gist of United’s claim, therefore, is that it should be accorded a greater role in the Board’s investigation. This argument must be rejected. Here United participated in the proceeding establishing the craft or class in question as a cognizable grouping of employees, and it has had opportunities since that time to present further evidence. It must be remembered that United is under no compulsion to reach an agreement with the certified representative. As Chief Justice Stone said in Virginian R. Co. v. System Federation No. 40, supra, “The quality of the action compelled, its reasonableness, and therefore the lawfulness of the compulsion, must be judged in the light of the conditions which have occasioned the exercise of governmental power.” Id., at 558-559. Likewise, as the Court observed in Hannah v. Larche, 363 U. S. 420, 442 (1960), the procedural requirements in a particular proceeding depend on “[t]he nature of the alleged right involved, the nature of the proceeding, and the possible burden on that proceeding ....” The Board, as we noted in Switchmen’s Union, performs the “function of a referee.” It does not select one organization or another; it simply investigates, defines the scope of the electorate, holds the election and certifies the winner. Thus, while the Board’s investigation and resolution of a dispute in one craft or class rather than another might impose some additional burden upon the carrier, we cannot say that the latter’s interest rises to a status which requires the full panoply of procedural protections. We find support for this conclusion when we consider the burden that acceptance of United’s contentions would visit upon the administration of the Act. To require full-dress hearings on craft or class in each representation dispute would fly in the face of Congress’ instruction that [668]*668representatives should be certified within 30 days of invocation of the Board’s services. It places beyond reach the speed which the Act’s framers thought an objective of the first order.
In view of these considerations, we hold that the Board performed its statutory duty to conduct an investigation and designate the craft or class in which the election should be held and that it did so in a manner satisfying any possible constitutional requirements that might exist. Its determination, therefore, is not subject to judicial review. Switchmen’s Union v. National Mediation Board, supra. As was pointed out there, the “highly selective manner in which Congress has provided for judicial review of administrative orders or determinations under the Act,” id., at 305, indicates the confidence that it reposed in the Board. In turn the fair and equitable manner in which the Board has discharged its difficult function is attested by the admirable results- it has attained.
4. The Form of the Ballot.
As we have noted the District Court enjoined the Board from conducting an election with a ballot that did not permit an employee to cast a vote against collective representation. We believe this was error. Section 2, Ninth empowers the Board to establish the rules governing elections. Moreover, it provides that in resolving representation disputes the Board is authorized “to take a secret ballot of the employees involved, or to utilize any other appropriate method of ascertaining the names of their duly designated and authorized representatives in such manner as shall insure the choice of representatives by the employees without interference, influence, or coercion exercised by the carrier.” Thus, not only does the statute fail to spell out the form of any ballot that might be used but it does not even require selection by ballot. It leaves the details to the broad dis[669]*669cretion of the Board with only the caveat that it “insure” freedom from carrier interference. That the details of ■ selecting representatives were to be left for the final determination of the Board is buttressed by legislative history clearly indicating as much.5 See Hearings on H. R. 7650, House Committee on Interstate and Foreign Commerce, 73d Cong., 2d Sess., 34^35.
In summary, then, the selection of a ballot is a necessary incident of the Board’s duty to resolve disputes. The Act expressly says as much, instructing the Board alone to establish the rules governing elections. Thus, it is clear that its decision on the matter is not subject to judicial review where there is no showing that it has acted in excess of its statutory authority.
United and the Association, however, apparently relying on Leedom v. Kyne, supra, contend that the Board has exceeded its statutory authority in selecting the proposed ballot. The argument is that § 2, Fourth, which provides that “[t]he majority of any craft or class of employees shall have the right to determine whp shall be the representative of the craft or class” requires a ballot with [670]*670a “no union” box. They urge that in Virginian B. Co. v. System Federation No. 40, supra, at 560, certification on the basis of a majority of the votes cast, rather than a majority of the eligible voters, was upheld on the ground that nonvoters “are presumed to assent to the expressed will of the majority of those voting.” And they say that the Board’s ballot is inconsistent with this rationale. But the Board has not followed the presumption of Virginian R. Co. Indeed the caveat on the face of the proposed ballot expressly refutes such an assumption. The Board’s rule of election procedure is that no vote is a vote for no representation, and this is now made plain to the voting employees. It is, as we have said, an assumption more favorable to the employees that the Association represents. Thus, under the Board’s practice a majority of the craft or class, as required by § 2, Fourth, does have the right to determine who shall be the representative of the group or, indeed, whether they shall have any representation at all.
It is also claimed that since § 9 (a) of the National Labor Relations Act, 49 Stat. 453, as amended, 61 Stat. 143, 29 U. S. C. § 159 (a) (1958 ed.) and § 2, Ninth of the Railway Labor Act are both designed to encourage collective bargaining and the National Labor Relations Board uses a ballot with a “no union” box, the Mediation Board must use one also. Even assuming that the “no union” ballot would implement the purpose of the Act, this is a far cry from saying that it is the only form of ballot that would do so. Given broad discretion as it is the Mediation Board has followed a presumption contrary to that adhered to by the Labor Relations Board. The latter has tailored its ballot to conform to the presumption of Virginian R. Co. If in a Labor Board election, an employee does not vote, he can safely be presumed to have acquiesced in the will of the majority of the voters. In a Mediation Board election, if the em[671]*671ployee refuses to vote he is treated as having voted for no representation.
We venture no opinion as to whether the Board’s proposed ballot will best effectuate the purposes of the Act. We do say that there is nothing to suggest that in framing it the Board has exceeded its statutory authority.
Unable to point to any specific requirement of a “no union” ballot in the Act, United and the Association are left to arguing in terms of policy and broad generalities as to what the Railway Labor Act should provide. The very nature of the arguments indicates that the Board’s choice of its proposed ballot is not subject to judicial review, for it was to avoid the haggling and delays of litigation that such questions were left to the Board. These are matters for Congress and the Board rather than the courts. Here the Board — a creature of Congress — has been, as we have said, careful to provide fair, yet effective procedures and we feel certain that it will continue to do so. If its decision on the ballot is not acceptable, the place to go is to Congress, not to us.
Accordingly, we reverse the judgments in Nos. 138 and 369 and affirm the judgment in No. 139.
It is so ordered.
Mr. Justice Black concurs in the result.