RALPH B. GUY, Jr., Circuit Judge.
Arguing preemption under federal labor law, defendant employer appeals the remand to state court of former employees’ claims challenging their discharge. The thrust of plaintiffs’ suit, which had been removed from state to federal court, was that defendants had fired them for attempting to organize and join the United Mine Workers Union. We do not reach the preemption issue because our review of the record causes us to conclude that we lack jurisdiction to consider this appeal, and accordingly dismiss it.
I.
The thirteen plaintiffs were formerly employed by defendant Kentucky-Ohio Transportation, Inc. (KOT), a wholly owned subsidiary of defendant Island Creek Corporation (Island Creek). Plaintiffs had signed union authorization cards and had otherwise been active in efforts to unionize KOT’s South Shore facility. The United Mine Workers Union represented other Island Creek employees, but the collective bargaining agreement did not cover these plaintiffs. After their termination, following the sale of the South Shore facility, plaintiffs filed a complaint with the National Labor Relations Board alleging the same facts and claims asserted in the current matter. At some unspecified time, but apparently before plaintiffs initiated the present suit,1 the NLRB declined to file a complaint against defendants. Plaintiffs did not appeal the board's decision.
Instead, plaintiffs filed a wrongful discharge and breach of contract suit in Kentucky court, claiming that their termination violated public policy in favor of the right to organize and contravened certain company policies and procedures as expressed in the employee handbook. Plaintiffs also claimed that the United Mine Workers Union breached its duty of fair representation for, among other things, failing to protect their jobs. The complaint also alleged that KOT, Island Creek, and the union acted in bad faith in failing to honor an alleged agreement that the union would be deemed the collective bargaining unit for KOT em[1343]*1343ployees when a majority of them signed union authorization cards.2
Defendants removed the case to federal court on the basis of federal question jurisdiction. The defendant corporations then moved for dismissal or summary judgment, arguing that the challenged actions were essentially unfair labor practices and required the interpretation of a collective bargaining agreement, and were therefore preempted by federal labor law. Finding that the NLRB had not designated the union as the exclusive bargaining representative for KOT employees, the district court dismissed the action against the union.
The district court then agreed that the state law claims against KOT and Island Creek essentially amounted to unfair labor practices under 29 U.S.C. §§ 157 and 158, such as to fall within the exclusive jurisdiction of the NLRB. The court concluded, however, that the NLRB’s refusal to issue a complaint left the Kentucky courts “free to hear the present matter on applicable state law theories.” Believing that the claims for wrongful discharge, breach of contract, and outrageous conduct could be resolved only by reference to state law, the court stated that it “lack[ed] subject matter jurisdiction” and remanded the case “pursuant to 28 U.S.C. § 1447 for proper disposition under Kentucky law.”
KOT and Island Creek appeal the remand order, requesting that this court order the case returned to the district court for dismissal on grounds of preemption.3 The union is not a party to this appeal.
II.
Although plaintiffs do not contest defendants’ claim that this court has authority to consider this appeal, we are obligated to ensure that we have jurisdiction over this matter. An order of remand on jurisdictional grounds is neither a final judgment for purposes of 28 U.S.C. § 1291 nor a ruling falling within the “collateral order” exception to that rule. Beard v. Carrollton R.R., 893 F.2d 117, 120 (6th Cir.1989). More importantly, however, we face the seemingly ironclad bar to review— no matter how the appeal is fashioned— which is contained in 28 U.S.C. § 1447(d). With an exception not relevant here, § 1447(d) declares: “An order remanding a case to the State court from which it was removed is not reviewable on appeal or otherwise....” If this statute meant what is says, that would be an end of the matter and our review clearly would be foreclosed.
The Supreme Court stated long ago, however, that the § 1447(d) proscription is not as broad as it seems. In Thermtron Products, Inc. v. Hermansdorfer, 423 U.S. 336, 96 S.Ct. 584, 46 L.Ed.2d 542 (1976), the district judge had remanded a diversity suit due to the crowded federal docket. The judge did not question the jurisdictional propriety of the removal. Relying on § 1447(d), the Sixth Circuit refused to consider the defendant’s mandamus petition, which requested' relief on the ground that the district judge had been powerless to order remand for the reason he had given.
The Supreme Court reversed, holding that § 1447(d) precludes review only of those remand orders issued pursuant to § 1447(c). As § 1447(c) then read:
If at any time before final judgment it appears that the case was removed improvidently and without jurisdiction, the district court shall remand the case....4
In Thermtron, the district judge had not purported to remand on a § 1447(c) basis; the statute was never mentioned and there was no suggestion that the case had been removed “improvidently and without jurisdiction.” Since the remand had instead been based “on grounds wholly different from those upon which § 1447(c) permits [1344]*1344remand,” 423 U.S. at 344, 96 S.Ct. at 589, the judge had exceeded his authority and the remand order was reviewable.
In Carnegie-Mellon University v. Cohill, 484 U.S. 343, 108 S.Ct. 614, 98 L.Ed.2d 720 (1988), the Court reaffirmed that the facially unequivocal language of § 1447(d) does not, in fact, preclude review of all remand orders. The district court in that case had remanded pendent state claims after the plaintiffs had withdrawn their lone federal claim. Remand had not been predicated on any provisions in the removal statutes. Section 1447(c) did not apply because removal of the case (federal and related state claims together) had been proper, and § 1441(c), authorizing discretionary remand of “separate and independent” claims, did not apply because the state claims had been pendent to the federal claim. Reviewing this non-statutorily-based remand, the Supreme Court resolved a circuit split and clarified that the doctrine of pendent jurisdiction does indeed allow district courts to remand pendent state claims. The Court repudiated Therm-tron ’s implication that remand orders could be based only on the grounds specified in the removal statute. Carnegie-Mellon, 484 U.S. at 355-56, 108 S.Ct. at 621-22. Finally, since the remand had not been based on § 1447(c), it was subject to review by extraordinary writ.
Since Thermtron, appellate courts have paved other detours around § 1447(d)’s bar to review. Under the so-called Pelle-port/Clorox doctrine first advanced by the Ninth Circuit, a remand based upon the district court’s resolution of “a substantive [issue] on the merits apart from any jurisdictional decision” was reviewable as a final order. Pelleport Investors, Inc. v. Budco Quality Theatres, 741 F.2d 273, 276 (9th Cir.1984). The remand in Pelleport — a diversity case — was not based on lack of subject matter jurisdiction or any defect in removal but, rather, on the court’s determination that the parties’ forum-selection agreement was enforceable. To immunize this variety of remand orders from review “would deprive [the objecting party] of its right to appeal a substantive determination of contract law,” a determination that was conclusive on the parties. Id. at 277. The court noted that the policy behind § 1447(d) is to prevent parties from using “the appeal process to protract litigation over jurisdictional issues.” Id. This policy is “inapplicable," however,
where a district court bypasses the jurisdictional arguments and reaches the merits of a contract dispute.... Any delay caused by an appeal of the contract issue is a delay which must be countenanced.
Id.
The Ninth Circuit subsequently relied on Pelleport to review a remand order that had been based on a district court’s conclusion that the defendant had contractually waived its removal rights. Clorox Co. v. United States Dist. Court, 779 F.2d 517 (9th Cir.1985). Like the remand in Pelle-port, the Clorox remand turned on the consideration of a collateral, non-jurisdictional issue, and thus fell outside the purview of § 1447(d).
This circuit endorsed the Ninth Circuit’s reasoning, concluding that § 1447(d) did not bar review of a remand order issued after a hearing on the validity of a forum-selection clause. In Regis Associates v. Rank Hotels (Management) Ltd., 894 F.2d 193 (6th Cir.1990), we agreed that a remand order is reviewable “when it is based on a substantive decision on the merits of a collateral issue as opposed to just matters of jurisdiction.” Id. at 194.
The Third Circuit recently recognized another variety of reviewable remand orders in In re TMI Litigation Cases Consolidated II, 940 F.2d 832 (3d. Cir.1991), cert. denied, — U.S. -, 112 S.Ct. 1262, 117 L.Ed.2d 491 (1992). Following a comprehensive inquiry into the history of § 1447(d) and its exceptions, the court concluded it had authority to review a remand order which was based on the district court’s belief that the statute investing federal courts with jurisdiction over certain public liability actions was unconstitutional.5 The court acknowledged that the dis[1345]*1345trict court had indeed remanded the case for what it (albeit erroneously) saw as a lack of subject matter jurisdiction — and thus, unlike the Pelleport/Clorox line of cases, the district court’s “ ‘substantive decision’ ” was not “ ‘apart from any jurisdictional decision.’ ” In re TMI, 940 F.2d at 843 (quoting Pelleport, 741 F.2d at 276 (emphasis added by Third Circuit)). Moreover, the district court had explicitly cited § 1447(c) as the statutory authority for the remand order.
Even though the “heart of this [substantive] decision was jurisdictional,” however, the TMI court believed that Congress never intended that § 1447(d) would bar review of a “jurisdictional determination ... resting ... upon the conclusion that the entire statutory scheme authorizing removal is unconstitutional.” Id. at 845. The court explained that the § 1447(d) bar is raised only when the remand order is based on a conclusion that the jurisdictional requirements as set forth by Congress had not been met in the ease at hand. Here, however, the remand turned on the belief that Congress had no power to authorize federal court jurisdiction over such cases in the first place. While somewhat artful, this analysis was advanced in support of the entirely defensible view that “in enacting section 1447(d), Congress did not intend to vest the district courts with the authority to make final determinations regarding the constitutionality of federal statutes.” Id. at 843.
The Third Circuit’s decision and the forum selection cases along the Pelle-port/Clorox line reflect the prevailing view that § 1447(d)’s prohibition against appellate review is fairly narrow. But they are not the only word on the subject. In cases raising preemption concerns of the sort at issue here, although in a slightly different procedural setting, several circuits have concluded that they lacked jurisdiction to entertain the mandamus petitions challenging the orders.6
The Ninth Circuit, the very court which generated the “substantive decision” exception to § 1447(d), declined to review remand orders which had been based on a conclusion that federal law did not preempt claims that had been pleaded as state law causes of-actions. In Whitman v. Raley’s Inc. and its companion case, Krentz v. Connecticut General Life Insurance Co., 886 F.2d 1177 (9th Cir.1989), a suit alleging wrongful discharge (and other non-federal claims) and one alleging “tortious refusal to pay benefits” had been removed to federal court, the former because it ostensibly required interpretation of a collective bargaining agreement, the latter on the ground that it was an artfully pled ERISA claim. After removal, the district courts then granted the plaintiffs’ motions to remand, after concluding that the claims were not, after all, preempted by federal law.
It could not be doubted that the district courts had remanded for lack of subject matter jurisdiction, so that the orders would seem to fall within the § 1447(d) prohibition. The question, however, was “whether in the process of making that decision on the basis of lack of federal preemption, a substantive law determination was made that would bring these cases within the Clorox exception,” Whitman, 886 F.2d at 1180. To answer that question, the Ninth Circuit drew a helpful distinction between “complete preemption” and “the substantive defense of preemption.” Id. at 1181.
According to Whitman, when a district court, considering the removal of a suit alleging state law violations, decides whether “Congress intended a preemptive force so powerful as to displace entirely any state cause of action within the ambit of the federal cause of action,” the court is considering only a jurisdictional issue. Id. at 1180-81. The focus there is “on whether it was the intent of Congress to make the cause of action a federal cause of action and removable despite the fact that the ... complaint identifies only state claims.” Id. at 1181. This jurisdictional inquiry is [1346]*1346distinct from the question whether a legal defense of preemption may be raised. Whether the defendant has a valid preemption defense “would be a matter for trial” by a court that has concluded it has jurisdiction over the case. Id. “If the court rules that the claim is not ‘completely preempted/ the federal court lacks jurisdiction to rule on the substantive preemption defense.” Id.
Since the remands in the Whitman and Krentz cases were based on a determination that there was no complete preemption, the orders necessarily were pursuant to § 1447(c), which requires remand for lack of subject matter jurisdiction. Id. As such, the orders were unreviewable under Thermtron.7 To allay the resulting concerns about the preclusive effect of its preemption rulings, the Ninth Circuit emphasized that, once the district courts had determined that they had no jurisdiction over the cases, they had no authority to rule on substantive defenses. Id.
The Eleventh Circuit followed similar reasoning in declining to review remand orders that had turned on conclusions about preemption. In Glasser v. Amalgamated Workers Union, 806 F.2d 1539 (11th Cir.1986), the district court had remanded a suit charging a union with wrongful denial of insurance benefits. The case had been removed as arising under ERISA. The district court had then remanded the case on the ground that it lacked subject matter jurisdiction in that the claims, which also included breach of fiduciary duty and fraud allegations, were all state claims and the defendant’s federal claims were merely defenses.
The Eleventh Circuit noted that, while the district court had indeed engaged in a sort of “substantive” inquiry within the meaning of the Pelleport/Clorox exception, that inquiry was undeniably “related to the question of jurisdiction [rather than] the substantive rights of the parties.” Glasser, 806 F.2d at 1540. The order thus fell within the general rule against review. As did the Ninth Circuit in Whitman and Krentz, and again in Hansen v. Blue Cross of California, 891 F.2d 1384 (9th Cir.1989),8 the court concluded that the unre-viewable nature of the remand order would not foreclose further litigation concerning preemption. In finding that it lacked jurisdiction, the district court “did not reach the merits of the preemption argument,” and the state court was free to “rule that ERISA does preempt [plaintiffs’] state law claims and that [plaintiffs] must proceed” under that federal statute. Glasser, 806 F.2d at 1540.
The Fifth Circuit found a similar remand unreviewable, although for a slightly different reason. In Soley v. First National Bank of Commerce, 923 F.2d 406 (5th Cir.1991), the court was faced with an ambiguous remand order that seemed to be based on both a finding of lack of complete preemption and a belief that there could be no substantive defense of preemption. Id. at 409. Although it chose one basis over the other and construed the order as solely jurisdictional, the appeals court found dis-positive the district court’s reliance on § 1447(c). The § 1447(d) prohibition kicked in, according to Soley, “because the district court did not clearly and affirmatively state that it relied on a non-1447(c) ground.” Id. at 409. Like the Ninth and Eleventh Circuits, the Fifth Circuit took “comfort” in the knowledge that interpreting the order as purely jurisdictional “will have no preclusive effect on the state court’s consideration of the substantive preemption defense.” Id.
In a case decided before the Ninth Circuit’s articulation of the distinction between a remand based on complete preemp[1347]*1347tion and one reaching the merits of a preemption defense, the Eighth Circuit found it had jurisdiction to review an order remanding, for lack of preemption, a state claim for vexatious refusal to pay insurance benefits. In re Life Ins. Co. of North America, 857 F.2d 1190 (8th Cir.1988). According to the Eighth Circuit, the district court did not issue its order pursuant to § 1447(c). Id. at 1193 n. 1. As to the preclusive effect of the district court’s ruling that ERISA did not preempt the state claim, the court said it would be binding on the state court “as res judicata and the law of the case.” Id. at 1193.
The authority the Eighth Circuit cited in support of this conclusion, however, demonstrates the importance of the distinction between complete preemption and the preemption defense. The court quoted the Seventh Circuit’s declaration that, “ ‘when a lower federal court has jurisdiction over the subject matter and the parties, its adjudication is the law of the case and its judgment is binding on all other courts.... ” Id., quoting United States ex rel. Lawrence v. Woods, 432 F.2d 1072, 1076 (7th Cir.1970), cert. denied, 402 U.S. 983, 91 S.Ct. 1658, 29 L.Ed.2d 148 (1971) (emphasis added). But, as the Ninth, Eleventh, and Fifth Circuits have found, a remand for lack of complete preemption, that is, a remand for lack of subject matter jurisdiction in the district court, does not foreclose state-court litigation of the preemption defense. The Seventh Circuit’s conclusion regarding the binding nature of the district court’s rulings was specifically premised on the existence of subject matter jurisdiction in that lower court. That premise disappears when the remand order is based on lack of complete preemption.
As noted above, this circuit addressed the reviewability of remand orders when adopting the Pelleport/Clorox “substantive decision” exception to § 1447(d) in a case involving a forum selection clause. Regis, 894 F.2d 193. We also have had occasion to consider the reviewability of a remand order involving a district court’s preemption analysis. In Beard v. Carrollton R.R., 893 F.2d 117 (6th Cir.1989), plaintiff brought an action in state court against his former employer, the railroad, and the insurance company which had issued the group medical and life insurance policy covering railroad employees. The insurance coverage was mandated by a collective bargaining agreement negotiated under the federal Railway Labor Act. Count one alleged, among other things, wrongful failure to provide benefits; count two was for intentional and malicious interference with contractual rights and intentional infliction of emotional distress.
After removing the case to federal court, the Beard defendants sought to dismiss the claims as preempted by the Railway Labor Act. The court dismissed count one without prejudice and remanded count two to state court. Significantly, the court said that the removal of the case had been proper, “because count one was really a claim under the Railway Labor Act” and was completely preempted by it. Id. at 120. However, the court believed that as count two was only remotely related to the collective bargaining agreement, it lacked subject matter jurisdiction to decide the merits of that count.
Citing Thermtron, this court reasoned that the order would be unreviewable, even in mandamus, if it had been issued “under the authority of any statute.” 9 Beard, 893 F.2d at 121. Here, there were only two possible statutory bases for the remand. Section 1447(c) could not have been the basis, we said, since the court had specifically found that the case had not been “removed improvidently and without jurisdiction,” as the then-controlling version of the statute read. Id. Nor could the remand have been ordered pursuant to § 1441(c), which invests district courts with the authority to remand claims that are “separate and independent” from the removable claim. The judge did not state that he was exercising his § 1441(c) authority to remand these separate claims but, rather, that he “lack[ed] jurisdiction to de[1348]*1348cide the merits.” Id. Therefore, the remand order, mysterious as it was, could not have been issued on the basis of any statutory mandate and, under Thermtron, was not subject to the § 1447(d) bar to review.
A similarly opaque remand order was considered recently in In re Amoco Petroleum Additives Co., 964 F.2d 706 (7th Cir.1992). There, an employee and her union sued Amoco over its use of a video camera in the hallway outside the women’s locker room. The union sought a restraining order and the employee sought damages for invasion of privacy and emotional distress. Amoco removed the case, arguing that it required the interpretation of the collective bargaining agreement. After the plaintiffs’ first motion to remand was denied without explanation, Amoco filed a summary judgment motion and the union dropped out of the case. Then, also without explanation, the court granted the renewed motion for remand and declined to consider the summary judgment motion. Amoco filed a mandamus petition seeking review of this order.
Because the district judge had failed to indicate why he had remanded the case, the Seventh Circuit, like this court in Beard, was left to forage among the possible reasons to determine if the order was of the sort unreviewable under § 1447(d). The only plausible basis for this particular remand order, the court decided, was lack of subject matter jurisdiction. But fastening on this reason did not solve the riddle; the court had to know whether the judge had believed he lacked jurisdiction at the outset (i.e., at the time of removal), or whether he believed that the jurisdictional defect appeared later.10
The timing question is dispositive because, despite the change in the wording of § 1447(c) since Thermtron and many of the above cases, courts still read that section as authorizing remand when a district court determines that jurisdiction had been lacking at the time of removal, rather than later (following a jurisdictionally sound removal).11 Therefore, if the district judge in Amoco had thought that the removal had been jurisdictionally proper but that jurisdiction had “vanished” when the union dropped out, the remand — even though based on a finding of lack of jurisdiction— would be reviewable, as § 1447(c) envisions remands only for defective removals.12 In other words, if the district judge had thought that jurisdiction had been lacking all along, the order would be beyond appellate review.
Since it was the only way to reconcile the district court’s earlier order denying the [1349]*1349plaintiffs’ remand motion with the later order granting the remand motion after the union dropped out, the Seventh Circuit concluded that the district judge must have thought that removal — with the union as a plaintiff — had been jurisdictionally proper, but that jurisdiction vanished with the union’s exit from the case. The court therefore proceeded to consider the propriety of the remand order.
III.
Unfortunately, we must play the same sort of guessing game in the present case. We do know that the order was based on the judge’s belief that the court “lacks subject matter jurisdiction.” We also know that the judge explicitly cited § 1447,13 unlike the orders considered in Beard and Amoco. It is unclear, however, whether the district judge believed that he lacked jurisdiction all along, or whether he had somehow lost jurisdiction following a proper removal. Nor is it clear that an answer to that question would solve the problem, as it did in Amoco, given the judge’s explicit invocation of § 1447.
Looking behind the face of the order, as we allowed ourselves to do in Beard, it is possible to infer that the judge believed that removal had indeed been proper. He did, after all, exercise authority over the case when he dismissed the claims against the union. However, his subsequent finding of a lack of jurisdiction was not tied to the exit of the union.14 Rather, it followed from a determination that the NLRB’s refusal to issue a complaint left the state court “free to hear the present matter on applicable state law theories,” and from a belief that state law governed the interpretation of the collective bargaining agreement.
As it appears that the NLRB’s refusal preceded the initiation of this suit, we cannot infer that the judge found it a post-removal, jurisdiction-defeating event (like the post-removal withdrawal of the union in Amoco). Nor would the judge’s conviction that state law governs the interpretation of the union contract have sprung from anything that followed removal; nothing indicates that he would not have held that conviction at the outset. Therefore, while it is tempting to adopt Amoco’s approach and find the remand reviewable as based on a belief (however erroneous) that a post-removal event had destroyed jurisdiction, the facts of this case are not amenable to such a resolution.
Defendants invite us to find that the Pelleport/Clorox “substantive decision” doctrine would permit review of the remand order here. The district court's decision was “based on a substantive decision on the merits of a collateral issue,” according to defendants. This reasoning is too facile. We find that the so-called “collateral issue” was not collateral at all within the meaning of the Pelleport/Clorox exception to § 1447(d). The preemption inquiry here, unlike an inquiry into the enforceability of a forum-selection clause, necessarily “related to the question of jurisdiction.” Glasser, 806 F.2d at 1540. Or, as the Third Circuit put it, “the heart of this decision was jurisdictional.” In re TMI, 940 F.2d at 843.15 We therefore cannot invoke the help of the “substantive decision” doctrine in this case.
[1350]*1350What we are left with, then, is the district court's explicit reference to § 1447 as the authority for remanding the case for lack of subject matter jurisdiction. This citation, absent in Amoco, Beard, and In re Life Insurance Co. of North America, 857 F.2d 1190 (8th Cir.1988), was deemed dis-positive in Soley. And, although the judge did exercise jurisdiction over the case when he dismissed the claims against the union, we have no explicit finding that removal had been proper. In this regard, the present case is again distinguishable from Beard, in which we found the order reviewable.
We therefore interpret this order as falling within the general category of remands specifically invoking the authority of § 1447(c), and thus subject to the well settled rule that § 1447(d) “prohibits review of all remand orders issued pursuant to § 1447(c) whether erroneous or not....” Thermtron, 423 U.S. at 343, 96 S.Ct. at 589. See also Gravitt v. Southwestern Bell Tel. Co., 430 U.S. 723, 97 S.Ct. 1439, 52 L.Ed.2d 1 (1977). In so concluding, we are guided by the policy, manifest in § 1447(d), of “preventing] delay in the trial of remanded cases by protracted litigation of jurisdictional issues_” Thermtron, 423 U.S. at 351, 96 S.Ct. at 593 (citation omitted). As we interpret the district court’s findings to be purely jurisdictional, the defendants may raise the merits of their preemption defense in state court.
Accordingly, we DISMISS this appeal for lack of jurisdiction pursuant to 28 U.S.C. § 1447(d).