26 U.S.C. § 7653: Shipments from the United States

All articles of merchandise of United States manufacture coming into Puerto Rico shall be entered at the port of entry upon payment of a tax equal in rate and amount to the internal revenue tax imposed in Puerto Rico upon the like articles of Puerto Rican manufacture. There shall be imposed in the Virgin Islands upon articles imported from the United States a tax equal to the internal revenue tax imposed in such islands upon like articles there manufactured. Articles, goods, wares, or merchandise going into Puerto Rico, the Virgin Islands, Guam, and American Samoa from the United States shall be exempted from the payment of any tax imposed by the internal revenue laws of the United States. All provisions of law for the allowance of drawback of internal revenue tax on articles exported from the United States are, so far as applicable, extended to like articles upon which an internal revenue tax has been paid when shipped from the United States to Puerto Rico, the Virgin Islands, Guam, or American Samoa. For the disposition of the proceeds of all taxes collected under the internal revenue laws of the United States on articles produced in Guam and transported into the United States or its possessions, or consumed in Guam, see the Act of August 1, 1950 ( 48 U.S.C. 1421h ).