P, a North Carolina corporation, brought this action in a North Carolina state court. P sued for damages for defamation. D, an unincorporated labor union whose principal place of business purportedly is Pennsylvania, removed the case to a Federal District Court. D asserted not only federal-question jurisdiction but that for purposes of the diversity jurisdiction, it was a citizen of Pennsylvania, although some of its members were North Carolinians. P moved to remand the case contending that its complaint raised no federal questions and relying upon the generally prevailing principle that an unincorporated association's citizenship is that of each of its members. The District Court retained jurisdiction. The Fourth Circuit reversed. D appealed.