Loewe v. Lawlor, 208 U.S. 274 (1908), also referred to as the Danbury Hatters' Case, is a United States Supreme Court case concerning the application of antitrust laws to labor unions. The Court's decision had the effect of outlawing secondary boycotts as violative of the Sherman Antitrust Act, in the face of labor union protests that their actions affected only intrastate commerce. It was also decided that individual unionists could be held personally liable for damages incurred by the activities of their union.

Prosecution of labor under antitrust laws would continue until the enactment of the Norris-La Guardia Act in 1932, which included express exemptions of organized labor from antitrust injunctions. These exemptions were upheld by the Supreme Court in United States v. Hutcheson (1941) where it was stated that the act should be read broadly to provide a total antitrust exemption for labor unions, "so long as union acts in its self-interest and does not combine with non-labor groups." The majority opinion in Hutcheson was written by Felix Frankfurter who, before becoming a Supreme Court Justice, had served as one of the drafters of Norris-La Guardia.