posse comitatus act
Posse Comitatus Act. A federal law that, with a few exceptions, prohibits the Army or Air Force from directly participating in civilian law-enforcement operations, as by making arrests, conducting searches, or seizing evidence. • The Act was originally enacted in 1878. It does not usu. apply to members of the Navy, the National Guard, or the Coast Guard. 18 USCA § 1385. — Abbr. PCA.