27 CFR §41.105

To prepay, in Puerto Rico, the internal revenue tax imposed by 26 U.S.C. 7652(a) on tobacco products and cigarette papers and tubes of Puerto Rican manufacture to be shipped to the United States, the shipper must file, or cause to be filed, a tax return, TTB F 5000.25, with full remittance of the tax which will become due on those products.