Each container of imported distilled spirits having a capacity of one gallon (3.785 liters) or less must have a closure or other device securely affixed to the container. The closure or other device must be constructed in such a manner as to require breaking in order to gain access to the contents of the container.
27 C.F.R. § 27.62
Sec. 454, Pub. L. 98-369, 98 Stat. 494 ( 26 U.S.C. 5301 )