In a decision that provides guidance on a previously “ill-defined” and “nebulous aspect of our federal courts’ jurisdiction,” the U.S. Court of Appeals for the Tenth Circuit clarified the cases in which federal courts may exercise ancillary enforcement jurisdiction and which law applies—10th Circuit Spotlightstate, federal, or both—when evaluating a plaintiff’s standing to bring such a case. Atlas Biologicals v. Kutrubes, No. 20-1401, 2022 U.S. App. LEXIS 28203, — F.4th — (10th Cir. Oct. 11, 2022).

The circuit court held “if a federal court had jurisdiction [over] the principal action, it may hear an ancillary proceeding, regardless of the citizenship of the parties, the amount in controversy, or any other factor that normally would determine subject matter jurisdiction” if the case is brought “to assist in the protection and enforcement of federal judgments—including attachment, mandamus, garnishment, and the prejudgment avoidance of fraudulent conveyances.” Id. at *19-20 (citations and quotations omitted). Because ancillary enforcement jurisdiction is a form of supplemental jurisdiction, the court also clarified that “the relevant state’s law of standing should be applied—in addition to federal standing law—in considering claims in such settings that are derived from state law.” Id. at *36-37.

The Principal Action