 Indeed, in 2004, the U.S. Supreme Court ruled in a unanimous decision “The Postal Service is not subject to antitrust liability.In both form and function, it is not a separate antitrust person from the United States but is part of the Government, and so is not controlled by the antitrust laws.” Sherman Antitrust Act.Unlike a state-owned enterprise, the USPS lacks a transparent ownership structure and isn't subject to standard rules and norms that apply to commercial entities.