Unless specifically exempt by statute, any agency or instrumentality of the United States, including post exchanges, ship's stores, ship's service stores, and commissaries, or any canteen, club, mess, or similar organization operated under regulations of any such agency or instrumentality, that sells, or offers for sale, distilled spirits, wines, or beer must comply with the registration and other requirements of this part as a dealer in liquors or a dealer in beer, as the case may be.

(26 U.S.C. 5121, 5122)