The Act Prohibiting the Return of Slaves is a law passed by the United States Congress during the American Civil War forbidding all officers or persons in the military or naval service to return escaped former slaves to their owners with the aid or use of the forces under their respective commands.

As Union armies entered Southern territory during the early years of the War, emboldened slaves began fleeing behind Union lines to secure their freedom. Some commanders put the escapees to work digging entrenchments, building fortifications, and performing other camp work. Such former slaves came to be called "contraband", a term emphasizing their status as captured enemy property. Other Army commanders returned the escapees to their owners. Congress reacted by approving this act which requires that any officer that violates the same to be dismissed from the service upon conviction by a court-martial.