In the United States Supreme Court case of United Steelworkers of America, AFL-CIO v. R.H. Bouligny, Inc., 1965, the court ruled that labor unions cannot be considered citizens for purposes of diversity jurisdiction in federal courts under U.S. law. The case arose when a North Carolina corporation sued a national labor union in state court over alleged violations of an agreement between them and sought damages and injunctions against strikes by union members at its plant. The union attempted to remove the suit to federal court on grounds that it was incorporated in another state (Pennsylvania), thus creating diversity jurisdiction - which allows cases between parties from different states to be heard in federal rather than state courts. However, the Supreme Court held that only natural persons or corporations can be treated as citizens for these purposes; other entities such as unincorporated associations or labor unions do not qualify despite their legal personality elsewhere within U.S law. The decision reinforced strict interpretation regarding who may invoke diversity jurisdiction while also emphasizing consistency and predictability within this area of jurisprudence.

In the dissenting opinion for United Steelworkers of America, AFL-CIO v. R.H. Bouligny, Inc., Justice Black argued that labor unions should be considered citizens of all states in which they have members for purposes of diversity jurisdiction. He disagreed with the majority's view that only natural persons or corporations could be deemed citizens under federal law and believed this interpretation was too narrow and inconsistent with previous court decisions recognizing other entities as "citizens." Furthermore, he contended that such a restrictive reading undermined Congress' intent to provide federal courts as forums for resolving disputes involving parties from different states. In his view, denying unions access to these courts simply because they are not traditional legal entities seemed unjustified and contrary to the spirit of diversity jurisdiction provisions.