Citigroup Global Markets, Inc. (CGMI) (plaintiff), a broker, sought to enjoin VCG Special Opportunities Master Fund, Ltd. (VCG) (defendant) from initiating an arbitration for claims arising from alleged violations of a credit-default swap agreement by CGMI’s affiliate, Citibank. The substantive question was whether VCG was a customer of CGMI for the purposes of the agreement. The federal district court granted CGMI’s motion for a preliminary injunction, finding that (1) CGMI had demonstrated a likelihood of irreparable harm, (2) CGMI had not shown a likelihood of success on the merits, (3) CGMI had nevertheless raised serious questions about the merits of VCG’s claim, and (4) the balance of hardships tipped decidedly in CGMI’s favor. Because CGMI had raised serious questions and the balance of hardships tipped decidedly in its favor, the district court granted the injunction. VCG appealed, arguing that the district court had used the wrong standard and could not grant a preliminary injunction unless CGMI demonstrated a likelihood of success on the merits. In support, VCG cited various United States Supreme Court cases, claiming that the cases abrogated the serious-questions standard applied by the district court.