394 BLACKMUN, J., concurring in judgment cata must give way to what the Court of Appeals referred to as "overriding concerns of public policy and simple justice.” 611 F. 2d 1267, 1269 (CA9 1980). Professor Moore has noted: "Just as res judicata is occasionally qualified by an overriding, competing principle of public policy, so occasionally it needs an equitable tempering." 1B J. Moore & T. Currier, Moore's Federal Practice 0.405 [12], p. 791 (1980) (footnote omitted). See also Reed v. Allen, 286 U. S. 191, 209 (1932) (Cardozo, J., joined by Brandeis and Stone, JJ., dissenting) ("A system of procedure is perverted from its proper function when it multiplies impediments to justice without the warrant of clear necessity"). But this case is clearly not one in which equity requires that the doctrine give way. Unlike the nonappealing party in Reed, respondents were not "caught in a mesh of procedural complexities." Ibid. Instead, they made a deliberate tactical decision not to appeal. Nor would public policy be served by making an exception to the doctrine in this case; to the contrary, there is a special need for strict application of res judicata in complex multiple party actions of this sort so as to discourage "break-away" litigation. Cf. Reiter v. Sonotone Corp., 442 U. S. 330, 345 (1979). Finally, this is not a case "where the rights of appealing and non-appealing parties are so interwoven or dependent on each other as to require a reversal of the whole judgment when a part thereof is reversed." See Ford Motor Credit Co. v. Uresti, 581 S. W. 2d 298, 300 (Tex. Civ. App. 1979).* *The Court of Appeals' reliance, 611 F. 2d 1267, 1269 (CA9 1980), on Uresti; Kvenild v. Taylor, 594 P. 2d 972 (Wyo. 1979); and In re Estate of McDill, 14 Cal. 3d 831, 537 P. 2d 874 (1975), appears to me to be clearly misplaced. Unlike those cases, this is not one in which the appealing and nonappealing parties made competing claims to a single piece of property, see McDill, or in which reversal only as to the appealing party would have unjustly left the nonappealing party liable, see Kvenild, or without recourse on his cross-claim, see Uresti. BRENNAN, J., dissenting 452 U.S. Second, and in contrast, I would flatly hold that Brown I is res judicata as to respondents' state-law claims. Like the District Court, the Court of Appeals found that those statelaw claims were simply disguised federal claims; since respondents have not cross-petitioned from that judgment, their argument that this case should be remanded to state court should be itself barred by res judicata. More important, even if the state and federal claims are distinct, respondents' failure to allege the state claims in Brown I manifestly bars their allegation in Brown II. The dismissal of Brown I is res judicata not only as to all claims respondents actually raised, but also as to all claims that could have been raised. See Commissioner v. Sunnen, 333 U. S. 591, 597 (1948); Restatement (Second) of Judgments § 61.1 (Tent. Draft No. 5, Mar. 10, 1978). Since there is no reason to believe that it was clear at the outset of this litigation that the District Court would have declined to exercise pendent jurisdiction over state claims, respondents were obligated to plead those claims if they wished to preserve them. See id., § 61.1, Comment e. Because they did not do so, I would hold the claims barred. JUSTICE BRENNAN, dissenting. In its eagerness to correct the decision of the Court of Appeals for the Ninth Circuit, the Court today disregards statutory restrictions on federal-court jurisdiction, and, in the process, confuses rather than clarifies long-established principles of res judicata. I therefore respectfully dissent. I Respondent Floyd R. Brown' filed this class action (Brown II) against petitioners in California state court. The com 1 Since the action by respondent Moitie has been voluntarily dismissed, the only remaining issues concern the claims of respondent Brown. 394 BRENNAN, J., dissenting plaint stated four state-law causes of action: (1) fraud and deceit, (2) unfair business practices, (3) civil conspiracy, and (4) restitution. Plaintiffs' Complaint. ¶¶ 11-14. App. 99-101. It alleged "not less than $600" damages per class member, and in addition sought "appropriate multiple damages," exemplary and punitive damages, interest from date of injury, attorney's fees and costs, and other relief. Id., at 101-102. All four of the causes of action rested wholly on California statutory or common law; none rested in any fashion on federal law. Nonetheless, petitioners removed the suit to the United States District Court for the Northern District of California, where respondent Brown filed a motion to remand on the ground that his action raised no federal question within the meaning of 28 U. S. C. § 1441 (b). Respondent's motion was denied by the District Court, which stated that "[f]rom start to finish, plaintiffs have essentially alleged violations by defendants of federal antitrust laws." App. 192. The court reasoned that "[a]rtful pleading" by plaintiffs cannot "convert their essentially federal law claims into state law claims," and held that respondent's complaint was properly removed "because [it] concerned federal questions which could have been originally brought in Federal District Court without satisfying any minimum amount in controversy." Ibid. The court then dismissed the action, holding that, under the doctrine of res judicata, Brown II was barred by the adverse decision in an earlier suit in federal court (Brown I) involving "the same parties, the same alleged offenses, and the same time periods." Ibid. The Court of Appeals affirmed the District Court's decision not to remand, stating that "[t]he court below correctly held that the claims presented were federal in nature." 611 F. 2d 1267, 1268 (CA9 1980) (memorandum on denial of reconsideration). However, the Court of Appeals reversed the District Court's order of dismissal, and remanded for trial. 452 U.S. BRENNAN, J., dissenting II The provision authorizing removal of actions from state to federal courts on the basis of a federal question is found in 28 U. S. C. § 1441 (b): "Any civil action of which the district courts have original jurisdiction founded on a claim or right arising under the Constitution, treaties or laws of the United States shall be removable without regard to the citizenship or residence of the parties." Removability depends solely upon the nature of the plaintiff's complaint: an action may be removed to federal court only if a "right or immunity created by the Constitution or laws of the United States [constitutes] an element, and an essential one, of the plaintiff's cause of action." Gully v. First National Bank in Meridian, 299 U. S. 109, 112 (1936). An action arising under state law may not be removed solely because a federal right or immunity is raised as a defense. Tennessee v. Union & Planters' Bank, 152 U. S. 454 (1894). An important corollary is that "the party who brings a suit is master to decide what law he will rely upon and therefore does determine whether he will bring a 'suit arising under' the... law[s] of the United States" by the allegations in his complaint. The Fair v. Kohler Die & Specialty Co., 228 U. S. 22, 25 (1913); accord, Great Northern R. Co. v. Alexander, 246 U. S. 276, 282 (1918). Where the plaintiff's claim might 2 As the District Court acknowledged, Brown II could not be removed on the basis of diversity of citizenship, because the amount in controversy did not exceed $10,000. App. 190. The court correctly noted, however, that the action could have been removed without regard to the amount in controversy, if it could have been brought as an original action in federal court without meeting any minimum amount in controversy. Ibid. Actions under the Clayton Act, 15 U. S. C. § 15, may be brought in federal court without regard to amount in controversy. See also Pub. L. 96-486, §§ 2 (a), 4, 94 Stat. 2369-2370, 28 U. S. C. § 1331 (1976 ed., Supp. IV), and note following § 1331 (repeal of minimum amount in controversy for federal-question cases pending as of date of enactment). 394 BRENNAN, J., dissenting be brought under either federal or state law, the plaintiff is normally free to ignore the federal question and rest his claim solely on the state ground. If he does so, the defendant has no general right of removal. Jones v. General Tire & Rubber Co., 541 F. 2d 660, 664-665 (CA7 1976); La Chemise Lacoste v. Alligator Co., 506 F. 2d 339, 346 (CA3 1974), cert. denied, 421 U. S. 937 (1975); Warner Bros. Records, Inc. v. R. A. Ridges Distributing Co., 475 F. 2d 262, 264 (CA10 1973); Coditron Corp. v. AFA Protective Systems, Inc., 392 F. Supp. 158, 160 (SDNY 1975). This corollary is well grounded in principles of federalism. So long as States retain authority to legislate in subject areas in which Congress has legislated without pre-empting the field, and so long as state courts remain the preferred forum for interpretation and enforcement of state law, plaintiffs must be permitted to proceed in state court under state law. It would do violence to state autonomy were defendants able to remove state claims to federal court merely because the plaintiff could have asserted a federal claim based on the same set of facts underlying his state claim. As this Court stated in Shamrock Oil & Gas Corp. v. Sheets, 313 U. S. 100, 108-109 (1941): "The power reserved to the states under the Constitution to provide for the determination of controversies in their courts, may be restricted only by the action of Congress in conformity to the Judiciary Articles of the Constitution. 'Due regard for the rightful independence of state governments, which should actuate federal courts, requires that they scrupulously confine their own jurisdiction to the precise limits which the statute has defined.'" (Quoting Healy v. Ratta, 292 U. S. 263, 270 (1934).) The general rule that a plaintiff basing his claim solely on state law thereby avoids removal applies only where state substantive law has not been pre-empted by federal law. "[W]here the plaintiff has a right to relief either under |