Posse Comitatus Act of 1879

Military personnel assigned to defense intelligence entities are subject to the Posse Comitatus Act, which provides that:


 * Whoever, except in cases and under circumstances expressly authorized by the Constitution or Act of Congress, willfully uses any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws shall be fined under this title or imprisoned not more than two years, or both.

Questions regarding which activities violate the Posse Comitatus Act arise most often in the context of assistance to civilian police. At least in that context, the courts have held that, absent a recognized exception, the Act is violated (1) when civilian law enforcement officials make “direct active use” of military investigators, (2) when the use of the military “pervades the activities” of the civilian officials, or (3) when the military is used so as to subject citizens to the exercise of military power that is “regulatory, prescriptive, or compulsory in nature.” The Act does not apply to the Navy or Marines and does not prohibit activities conducted for a military purpose that incidentally benefit civilian law enforcement bodies.