National Minimum Drinking Age Act
The National Minimum Drinking Age Act of 1984 (23 U.S.C. § 158) was passed by the United States Congress and was later signed into law by President Ronald Reagan on July 17, 1984. The act punished any state that allowed persons under 21 years to purchase alcoholic beverages by reducing its annual federal highway apportionment by 10 percent.
Source: Wikipedia — National Minimum Drinking Age Act (CC BY-SA 4.0)