23 CFR §1208.4

The Secretary shall withhold ten percent of the amount required to be apportioned to any State under each of §§ 104(b)(1), 104(b)(2), 104(b)(5) and 104(b)(6) of title 23 U.S.C. on the first day of each fiscal year in which the purchase or public possession in such State of any alcoholic beverage by a person who is less than twenty-one years of age is lawful.