 The Posse Comitatus Act is a United States federal law (18 U.S.C.§ 1385) passed on June 18, 1878, with the intention of substantially limiting the powers of the federal government to use the military for law enforcement.The act prohibits members of the Marine Corps, Army, Navy, Air Force, and state National Guard forces from exercising law enforcement powers, including those that maintain "law and order" within the United States.