Introduction

Supplemental Jurisdiction

Introduction

Suppose an employee sues a former employer in federal court under a federal anti-discrimination statute and, in the same complaint, adds a state-law claim for breach of the employment contract arising from the same firing. The federal claim presents a federal question, so the court plainly has power to hear it. The contract claim, however, involves two parties from the same state and no federal issue, so standing alone it has no basis for federal jurisdiction. Subject-matter jurisdiction is ordinarily tested claim by claim, yet the Federal Rules encourage a litigant to join related claims in one lawsuit. If the court had to split the case along jurisdictional lines, the plaintiff would be forced to try one set of facts twice, once in each system.

Supplemental jurisdiction resolves that tension by allowing a federal court to hear a claim that lacks its own jurisdictional basis when it is closely tied to a claim that has one. Two layers of authority are involved, and they must be kept apart. Article III of the Constitution sets the outer limit on what federal courts may hear, and the Supreme Court defined that limit in United Mine Workers of America v. Gibbs, which allows a federal court to hear a state claim that shares a common nucleus of operative fact with the federal claim, so that a plaintiff would ordinarily be expected to try them all in one proceeding.¹ Congress must then actually confer that power by statute, and it did so in 28 U.S.C. § 1367(a). In any civil action of which the district courts have original jurisdiction, the statute gives them supplemental jurisdiction over all other claims so related to the original-jurisdiction claims that they form part of the same case or controversy under Article III, and that grant extends to claims involving the joinder or intervention of additional parties.²

The first analytical step follows from the statute's opening words. Before asking whether a second claim is related, the court must find at least one claim in the action that satisfies a standalone basis such as federal question or diversity, because supplemental jurisdiction attaches to that anchor claim and cannot create jurisdiction where none exists. Only then does the question of relatedness arise. The statute's grant is expressly subject to two further limits: § 1367(b) takes back part of the grant in cases founded solely on diversity,³ and § 1367(c) lets a court decline jurisdiction it otherwise has.⁴ This chapter follows that order: why the doctrine exists, the constitutional baseline from Hurn v. Oursler through Gibbs, the statutory grant, the diversity restrictions and their interpretation in Exxon Mobil Corp. v. Allapattah Services, the court's discretion to decline, and the remaining statutory details. It begins with the problem that all of this machinery was built to solve.