MBE Rules · Civil Procedure
Supplemental Jurisdiction — Plaintiff Limits
28 U.S.C. §1367(b)
The rule
In diversity-only cases there is no supplemental jurisdiction over claims by plaintiffs against parties joined under Rules 14, 19, 20, or 24 when it would defeat complete diversity — defendant claims are unaffected.
In plain English
Supplemental jurisdiction allows a federal court to hear additional claims related to a case, but in diversity-only cases, plaintiffs cannot use it to bring in claims against new parties if doing so would destroy complete diversity. This means that if a plaintiff tries to add a defendant from the same state as themselves, the court cannot hear that claim. However, claims by defendants against plaintiffs are still allowed under supplemental jurisdiction.
Worked example
In a diversity case where Plaintiff A from California sues Defendant B from Texas, Plaintiff A tries to add Defendant C, who is also from California, to the lawsuit. Since adding Defendant C would destroy complete diversity, the court cannot exercise supplemental jurisdiction over that claim. Therefore, the claim against Defendant C is dismissed.
Memory hook
No diversity, no supplemental jurisdiction for plaintiffs!
The trap
Exams may present scenarios where students mistakenly believe they can add parties under supplemental jurisdiction without considering the impact on diversity. Watch for fact patterns that hint at diversity issues.
How examiners test it
This rule often appears in questions involving multiple parties where students must analyze the implications of adding new defendants on diversity jurisdiction. Look for clues indicating the states of the parties involved.
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