The Anti-Injunction Act (28 U.S.C. § 2283), is a United States federal statute that restricts a federal court's authority to issue an injunction against ongoing state court proceedings, subject to three enumerated exceptions. It states: A court of the United States may not grant an injunction to stay proceedings in a state court except as expressly authorized by Act of Congress, or where necessary in aid of its jurisdiction, or to protect or effectuate its judgments.