[299]*299Mr. Justice Marshall
delivered the opinion of the Court.
In this cause we are asked to determine whether strikes by Operating Engineers at the site, of the construction of a nuclear power generator plant at Oyster Creek, New Jersey, violated § 8 (b) (4) (B)1 of the National Labor Relations Act. Although the National Labor Relations Board, found the strikes to be in violation of this section, the Court of Appeals refused to enforce the Board’s order.2 We believe the Court of Appeals construed the Act too narrowly. Accordingly, we reverse and remand the case for consideration of the propriety of the Board’s order.
[300]*300The general contractor for the project, Burns & Roe, Inc., subcontracted all of the construction work to three companies — White Construction Co., Chicago Bridge & Iron Co., and Poirier & McLane Corp. All three employed operating engineers who were members of Local 825, International Union of Operating Engineers. But White, unlike Chicago Bridge and Poirier, did not have a collective-bargaining agreement with Local 825.
In the latter part of September 1965, White installed an electric welding machine and assigned the job of pushing the buttons that operated the machine to members of the Ironworkers Union, who were to perform the actual welding. Upon learning of this work assignment, Local 825’s job steward and its lead engineer threatened White with a strike if operating engineers were not given the work. White, however, refused to meet the demand. On September 29, 1965, the job steward and lead engineer met with the construction manager for Burns, the general contractor. They informed him that the members of Local 825 working at the jobsite had voted to strike unless Burns signed a contract, which would be binding3 on all three subcontractors as well as Burns, giving Local 825 jurisdiction over all power equipment, including electric welding machines, operated on the job-site. On October 1, after White and Burns refused to [301]*301accede to the demands, the operating engineers employed by Chicago Bridge and Poirier as well as those employed by White walked off the job. They stayed out from 8 a. m, to 1 p. m., returning to work when negotiations over their demands started.
On October 6, Burns submitted the work assignment dispute to the National Joint Board for the Settlement of Jurisdictional Disputes for the Construction Industry.4 The shme day, Local 825 threatened Burns and all the subcontractors with another work stoppage unless the contracts were signed and the work transferred to the operating engineers. The employers again refused, and the operating engineers walked off the project. This stride lasted from October 7 to October 11.
On October 20, the Joint Board notified the parties • that there was no reason to change the assignment of the. disputed, work. Local 825 did not accept this resolution; and when the welding machine was started on "November 4, the operating engineers surrounded the machine and physically prevented its operation. On November 8, the NLRB Regional Director obtained from the United States District Court a temporary injunction under § 10 (l)5 of the Act restraining the union from coercing a cessation of business on the project or to compel White to change the work assignment.6
[302]*302An unfair labor practice proceeding against Local 825 subsequently ensued. The Board found.that the union had violated §8 (b)(4)(D)7 of the Act by inducing employees of White, Chicago Bridge, and Poirier to strike to force White to take the disputed work away from the Ironworkers and assign it to the Operating Engineers. The Court of Appeals’ approval of this finding is not questioned here. But the Board’s finding that Local 825’s encouragement of the Chicago Bridge and Poirier employees to strike and the union’s coercion of Burns violated § 8 (b) (4) (B) of the Act. was not approved by the Court of Appeals and is in issue here.
I
Congressional concern over the involvement of third parties in labor disputes not their own prompted § 8 (b) (4)(B). This concern was focused on the “secondary boycott,” 8 which was conceived of as pressure brought to [303]*303bear, not “upon the employer who alone is a party [to a dispute], but upon some third party who has no concern in it” 9 with the objective of forcing the third party to bring pressure on the employer to agree to the union’s demands.10
Section 8 (b) (4)(B) is, however, the product of legislative compromise and also reflects a concern with protecting labor organizations’ right to exert legitimate pressure aimed at the employer with whom there is a primary dispute.11 This primary activity is protected even though it may seriously affect neutral third parties. Steelworkers (Carrier Corp.) v. NLRB, 376 U. S. 492, 502 (1964); Electrical Workers (General Electric) v. NLRB, 366 U. S. 667, 673 (1961).
Thus there are two threads to § 8 (b) (4) (B) that require disputed conduct to be classified as either “primary” or “secondary.” And the tapestry that has been woven in classifying such conduct is among the labor law’s most intricate. See Brotherhood of Railroad Trainmen v. Jacksonville Terminal Co., 394 U. S. 369 (1969). But here the normally difficult task of classifying union conduct is easy. As the Court of Appeals said, the “record amply justifies the conclusion that [Burns and the neutral subcontractors] were subjected to coercion in the [304]*304form of threats or walkouts, or both.” 410 F. 2d, at 9. And, as the Board said, it is clear that this coercion was designed “to achieve the assignment of [the] disputed work” to operating engineers. 162 N. L. R. B. 1617, 1621.
Local 825’s coercive activity was aimed directly at Burns and the subcontractors that were not involved in the dispute. The union engaged in a strike against these neutral employers for the specific, overt purpose of forcing them to put pressure on White to assign the job of operating the welding machine to operating engineers. Local 825 was not attempting to apply the full force of primary action by directing its efforts at all phases of Burns’ normal operation as was the case in Steelworkers (Carrier) v. NLRB, 376 U. S. 492 (1964), and Electrical Workers (General Electric) v. NLRB, 366 U. S. 667 (1961). It was instead using a sort of pressure that was unmistakably and flagrantly secondary. NLRB v. Denver Building & Construction Trades Council, 341 U. S. 675 (1951).
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[299]*299Mr. Justice Marshall
delivered the opinion of the Court.
In this cause we are asked to determine whether strikes by Operating Engineers at the site, of the construction of a nuclear power generator plant at Oyster Creek, New Jersey, violated § 8 (b) (4) (B)1 of the National Labor Relations Act. Although the National Labor Relations Board, found the strikes to be in violation of this section, the Court of Appeals refused to enforce the Board’s order.2 We believe the Court of Appeals construed the Act too narrowly. Accordingly, we reverse and remand the case for consideration of the propriety of the Board’s order.
[300]*300The general contractor for the project, Burns & Roe, Inc., subcontracted all of the construction work to three companies — White Construction Co., Chicago Bridge & Iron Co., and Poirier & McLane Corp. All three employed operating engineers who were members of Local 825, International Union of Operating Engineers. But White, unlike Chicago Bridge and Poirier, did not have a collective-bargaining agreement with Local 825.
In the latter part of September 1965, White installed an electric welding machine and assigned the job of pushing the buttons that operated the machine to members of the Ironworkers Union, who were to perform the actual welding. Upon learning of this work assignment, Local 825’s job steward and its lead engineer threatened White with a strike if operating engineers were not given the work. White, however, refused to meet the demand. On September 29, 1965, the job steward and lead engineer met with the construction manager for Burns, the general contractor. They informed him that the members of Local 825 working at the jobsite had voted to strike unless Burns signed a contract, which would be binding3 on all three subcontractors as well as Burns, giving Local 825 jurisdiction over all power equipment, including electric welding machines, operated on the job-site. On October 1, after White and Burns refused to [301]*301accede to the demands, the operating engineers employed by Chicago Bridge and Poirier as well as those employed by White walked off the job. They stayed out from 8 a. m, to 1 p. m., returning to work when negotiations over their demands started.
On October 6, Burns submitted the work assignment dispute to the National Joint Board for the Settlement of Jurisdictional Disputes for the Construction Industry.4 The shme day, Local 825 threatened Burns and all the subcontractors with another work stoppage unless the contracts were signed and the work transferred to the operating engineers. The employers again refused, and the operating engineers walked off the project. This stride lasted from October 7 to October 11.
On October 20, the Joint Board notified the parties • that there was no reason to change the assignment of the. disputed, work. Local 825 did not accept this resolution; and when the welding machine was started on "November 4, the operating engineers surrounded the machine and physically prevented its operation. On November 8, the NLRB Regional Director obtained from the United States District Court a temporary injunction under § 10 (l)5 of the Act restraining the union from coercing a cessation of business on the project or to compel White to change the work assignment.6
[302]*302An unfair labor practice proceeding against Local 825 subsequently ensued. The Board found.that the union had violated §8 (b)(4)(D)7 of the Act by inducing employees of White, Chicago Bridge, and Poirier to strike to force White to take the disputed work away from the Ironworkers and assign it to the Operating Engineers. The Court of Appeals’ approval of this finding is not questioned here. But the Board’s finding that Local 825’s encouragement of the Chicago Bridge and Poirier employees to strike and the union’s coercion of Burns violated § 8 (b) (4) (B) of the Act. was not approved by the Court of Appeals and is in issue here.
I
Congressional concern over the involvement of third parties in labor disputes not their own prompted § 8 (b) (4)(B). This concern was focused on the “secondary boycott,” 8 which was conceived of as pressure brought to [303]*303bear, not “upon the employer who alone is a party [to a dispute], but upon some third party who has no concern in it” 9 with the objective of forcing the third party to bring pressure on the employer to agree to the union’s demands.10
Section 8 (b) (4)(B) is, however, the product of legislative compromise and also reflects a concern with protecting labor organizations’ right to exert legitimate pressure aimed at the employer with whom there is a primary dispute.11 This primary activity is protected even though it may seriously affect neutral third parties. Steelworkers (Carrier Corp.) v. NLRB, 376 U. S. 492, 502 (1964); Electrical Workers (General Electric) v. NLRB, 366 U. S. 667, 673 (1961).
Thus there are two threads to § 8 (b) (4) (B) that require disputed conduct to be classified as either “primary” or “secondary.” And the tapestry that has been woven in classifying such conduct is among the labor law’s most intricate. See Brotherhood of Railroad Trainmen v. Jacksonville Terminal Co., 394 U. S. 369 (1969). But here the normally difficult task of classifying union conduct is easy. As the Court of Appeals said, the “record amply justifies the conclusion that [Burns and the neutral subcontractors] were subjected to coercion in the [304]*304form of threats or walkouts, or both.” 410 F. 2d, at 9. And, as the Board said, it is clear that this coercion was designed “to achieve the assignment of [the] disputed work” to operating engineers. 162 N. L. R. B. 1617, 1621.
Local 825’s coercive activity was aimed directly at Burns and the subcontractors that were not involved in the dispute. The union engaged in a strike against these neutral employers for the specific, overt purpose of forcing them to put pressure on White to assign the job of operating the welding machine to operating engineers. Local 825 was not attempting to apply the full force of primary action by directing its efforts at all phases of Burns’ normal operation as was the case in Steelworkers (Carrier) v. NLRB, 376 U. S. 492 (1964), and Electrical Workers (General Electric) v. NLRB, 366 U. S. 667 (1961). It was instead using a sort of pressure that was unmistakably and flagrantly secondary. NLRB v. Denver Building & Construction Trades Council, 341 U. S. 675 (1951).
The more difficult task is to determine whether one of Local 825’s objectives was to force Burns and the other neutrals to “cease doing business” with White as § 8 (b)(4)(B) requires. The Court of Appeals concluded that the union’s objective was to force Burns “to use its influence with the subcontractor to change the subcontractor’s conduct, not to terminate their relationship” and. that this was not enough. 410 F. 2d, at 10. That court read the statute as requiring that the union demand nothing short of a complete termination of the business relationship between the neutral and the primary employer. Such a reading is too narrow.
Some disruption of business relationships is the necessary consequence of the purest form of primary activity. These foreseeable disruptions are, however, clearly protected. Steelworkers (Carrier), 376 U. S., at 496; Electrical Workers (General Electric), 366 U. S., at 682. [305]*305Likewise, secondary activity could have such a limited goal and the foreseeable result of the conduct could be, while disruptive, so slight that the “cease doing business” requirement is not met.
Local 825’s goal was not so limited nor were the foreseeable Consequences of its secondary pressure slight. The operating engineers sought to force Burns to bind all the subcontractors on the project to a particular form of job assignments. The clear implication of the demands was that Burns would be required either to force a change in White’s policy or to terminate White’s contract. The strikes shut down the whole project. If Burns was unable to obtain White’s consent, Local 825 was apparently willing to continue disruptive conduct that would bring all the employers to their knees.
Certainly, the union would have preferred to have the employers capitulate to its demands; it wanted to take the job of operating the welding machines away from the Ironworkers. It was willing, however, to try to obtain this capitulation by forcing neutrals to compel White to meet union demands, To hold that this flagrant secondary conduct with these most serious disruptive effects was not prohibited by § 8 (b) (4) (B) would be largely to ignore the original congressional concern. NLRB v. Carpenters Dist. Council, 407 F. 2d 804, 806 (CA5 1969).
II
In addition to its argument that § 8 (b) (4) (B) does not cover its conduct, Local 825 argues that § 8. (b)(4)(D) provides’the exclusive remedy. Clearly, § 8 (b) (4) (D) is, as the Board and Court of Appeals held, applicable. But that section is aimed at protecting “the employer trapped between the ¡ . . claims” of rival unions. National Woodwork Mfrs. Assn. v. NLRB, 386 U. S. 612, 625 (1967). Although § 8(b)(4) (D) also [306]*306applies to neutrals, the basic purpose is different from that of §8 (b)(4)(B). The practices her'e were, unfair under both sections and there is no inaication that Congress intended either section to have exclusive application.
III
Since the Court of Appeals did not believe that § 8 (b) (4) (B) was applicable, it did not consider the propriety of the portion of the Board’s order relating to that section. But the order was not narrowly confined to the conduct;involved here; so we must remand these cases for the Court of Appeals to. consider whether the order is necessary to further the. goals of the Act. See Communications Workers v. NLRB, 362 U. S. 479 (1960); NLRB v. Express Publishing Co., 312 U. S. 426 (1941).
Reversed and remanded.