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 Union military or naval service to return escaped enslaved people to their enslavers with the aid or use of the forces under their respective commands.

As Union armies entered Confederate-occupied territory during the early years of the war, encouraged enslaved people began fleeing behind Union lines to secure their freedom.

Such people escaping slavery came to be called "contraband", a term emphasizing their status as captured enemy property.

Congress approved this act, requiring that any officer who violates the same be dismissed from the service upon conviction by a court-martial.

"An act to make an additional article of war" was approved March 13, 1862, with the following wording:[3]Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That hereafter the following shall be promulgated as an additional article of war for the government of the army of the United States, and shall be obeyed and observed as such: Article ––.