The case Royal Canin v. Wullschleger. The core issue revolves around whether a federal court retains supplemental jurisdiction after a plaintiff amends their complaint to remove all federal claims, particularly in cases initially brought in state court and then removed. Petitioners argue established precedent and Section 1367 support retaining jurisdiction, emphasizing the defendant's right to removal. Respondents contend the amended complaint should control, aligning with a principle that the operative pleading determines jurisdiction. The justices' questions explore the nuances of Section 1367, precedent (including Cohill and Rockwell), and the implications for various jurisdictional doctrines.