Anti-Injunction Act. A federal statute providing that a federal court may not enjoin state-court proceedings unless an injunction is (1) expressly authorized by Congress, (2) necessary for the federal court’s in rem jurisdiction, or (3) necessary to prevent relitigation of a judgment rendered by the federal court. 28 USCA § 2283. See NORRIS–LA GUARDIA ACT. [Cases: Courts 508. C.J.S. Courts §§ 216, 218–219.]