Supplemental Jurisdiction Flowchart: Anchor, Nucleus, Diversity, Discretion

A supplemental jurisdiction flowchart walks through four questions in order: is there an anchor claim the federal court can hear on its own, does the additional claim share a common nucleus of operative fact with it, do the diversity-only restrictions in 28 U.S.C. § 1367(b) block the claim, and would the judge decline jurisdiction under § 1367(c) even if the statute allows it. Work the steps in that sequence. Skip one and you can end up litigating in the wrong forum, or losing a claim entirely.

Step One: Is There an Anchor Claim?

Everything else depends on this. The court needs at least one claim it can hear on its own, through either federal question jurisdiction (the claim arises under a federal statute or the Constitution) or diversity of citizenship jurisdiction (the parties are from different states and more than $75,000 is at stake).¹ No qualifying anchor, no supplemental jurisdiction. The analysis ends there.

Think of the anchor as a hook. A federal employment discrimination claim can pull in a related state-law wrongful termination claim arising from the same firing, even though the state claim alone would never reach federal court. But the hook has to hold weight first.

Step Two: Do the Claims Share a Common Nucleus of Operative Fact?

Section 1367(a) extends supplemental jurisdiction to claims “so related” to the anchor that they form part of the same constitutional case or controversy.² The working test comes from United Mine Workers v. Gibbs: the claims must “derive from a common nucleus of operative fact.”³

In practice, that means the same underlying events, the same witnesses, the same evidence. A federal civil rights claim paired with a state-law battery claim from the same police encounter passes without difficulty. A state-law contract dispute from two years earlier, involving different parties and different facts, does not. The Gibbs court framed it this way: if a plaintiff would ordinarily try all the claims in one proceeding, the federal court has constitutional power to hear them together.³

This is the constitutional floor. Fail it and the court lacks power, no matter how convenient joint litigation would be. Pass it and you move on. Two more questions remain.

Step Three: Is This a Diversity-Only Case?

If the anchor claim rests on a federal question, skip ahead. If the anchor rests solely on diversity, Section 1367(b) adds restrictions designed to stop plaintiffs from using supplemental jurisdiction to sidestep the complete-diversity rule.²

In a diversity-only case, § 1367(b) bars supplemental jurisdiction over claims by plaintiffs against parties brought in through four procedural rules:

Rule 14 impleader, where a defendant brings in a third party for contribution or indemnity.⁴
Rule 19 required joinder, for parties who must be in the case for it to be fairly resolved.
Rule 20 permissive joinder, for parties who choose to join together.
Rule 24 intervention, for outside parties entering to protect their own interests.

In each situation, a plaintiff’s claim against that party is barred if it would defeat diversity. The statute also blocks supplemental jurisdiction over people seeking to join as plaintiffs under Rule 19 or intervene as plaintiffs under Rule 24 when doing so would undermine the § 1332 diversity requirements.² The point behind all of this is the same: a plaintiff shouldn’t be able to pick a diverse defendant to get into federal court and then use § 1367 to pull in the non-diverse party they really wanted to sue.

Defendants’ Claims Are Not Restricted the Same Way

Read § 1367(b) carefully. It restricts claims by plaintiffs. It says nothing about claims by defendants. A defendant’s compulsory counterclaim, crossclaim against a co-defendant, or third-party claim can qualify under § 1367(a) without running into § 1367(b).² A defendant did not choose the forum, so forcing a defendant to split related claims across two courts would be unfair. Compulsory counterclaims, which by definition arise from the same transaction or occurrence as the plaintiff’s claim, satisfy the common-nucleus test on their own terms.

Multiple Plaintiffs and the Amount in Controversy

In a diversity case with multiple plaintiffs, at least one named plaintiff must individually clear the $75,000 amount-in-controversy threshold. The Supreme Court held in Exxon Mobil Corp. v. Allapattah Services that once one plaintiff clears it, § 1367 authorizes supplemental jurisdiction over the claims of other plaintiffs in the same case or controversy, even if their individual claims fall below $75,000.⁵ That rule matters in multi-plaintiff cases and in class actions where unnamed members have small-dollar claims.

Step Four: Will the Judge Decline Anyway?

Clearing the statute does not force the court to hear the claim. Section 1367(c) gives federal judges discretion to decline supplemental jurisdiction in four situations:²

The supplemental claim raises a novel or complex issue of state law that a state court is better positioned to resolve.
The state-law claims substantially predominate over the federal anchor.
Every claim that gave the court original jurisdiction has been dismissed.
Other exceptional circumstances provide compelling reasons to decline.

The third ground is the one that comes up most often. When a federal claim falls out on a motion to dismiss or summary judgment early in the case, judges routinely refuse to keep the state-law claims. The further the litigation has progressed, the less willing a court will be to send the parties elsewhere to start over; a case already through discovery and near trial usually stays put.

If the Court Declines, What Happens to the Claims?

The answer depends on how the case reached federal court. If it was originally filed there, the judge dismisses the supplemental claims without prejudice and the plaintiff refiles in state court. If the defendant removed the case from state court, the judge may remand the remaining claims back under Carnegie-Mellon University v. Cohill, which is usually the cleaner outcome because the parties avoid a new filing.⁶

Section 1367(d) protects the plaintiff from losing claims to the statute of limitations while the federal case was pending. It tolls the limitations period on supplemental claims while they are in federal court and for 30 days after dismissal.² The Supreme Court confirmed in Artis v. District of Columbia that “toll” means the clock actually stops; the time remaining when the federal suit was filed is preserved, not simply replaced with a 30-day grace period.⁷ That 30-day window is enforced strictly. Miss it and viable claims die on the deadline.

Plead the Jurisdictional Basis

Federal Rule of Civil Procedure 8(a)(1) requires every pleading to include “a short and plain statement of the grounds for the court’s jurisdiction.”⁸ For supplemental claims, identify the anchor claim, cite § 1367 as the basis for the additional claims, and explain how the claims share the same case or controversy. A complaint that skips this invites a motion to dismiss and signals that the jurisdictional analysis above never happened.

1
Office of the Law Revision Counsel. 28 USC 1332 – Diversity of Citizenship
2
Office of the Law Revision Counsel. 28 USC 1367 – Supplemental Jurisdiction
3
Legal Information Institute. United Mine Workers v Gibbs, 383 US 715
4
Legal Information Institute. Federal Rules of Civil Procedure Rule 14 – Third-Party Practice
5
Justia U.S. Supreme Court Center. Exxon Mobil Corp v Allapattah Services Inc, 545 US 546
6
Justia U.S. Supreme Court Center. Carnegie-Mellon University v Cohill, 484 US 343
7
Justia U.S. Supreme Court Center. Artis v District of Columbia, 583 US ___ (2018)
8
Legal Information Institute. Federal Rules of Civil Procedure Rule 8 – General Rules of Pleading