The Posse Comitatus Act is a United States federal law ( ) passed on June 16, 1878 after the end of Reconstruction. The Act prohibits most members of the federal uniformed services (Army, Air Force, and State National Guard forces when such are called into federal service) from exercising nominally state law enforcement police or peace officer powers that maintain "law and order" on non-federal property (States, their counties and municipal divisions) in the former Confederate states.
The statute generally prohibits federal military personnel and units of the United States National Guard under federal authority from acting in a law enforcement capacity within the United States, except where expressly authorized by the Constitution or Congress. The Coast Guard is exempt from the Posse Comitatus Act.
The Posse Comitatus Act and the Insurrection Act substantially limit the powers of the federal government to use the military for law enforcement.
