U.S. ConstitutionArticle I — The Legislative BranchSubarticle 9Section 4
No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or enumeration herein before directed to be taken.
Use as reference
Lexinter.net | U.S. Const. art. I, § 9, cl. 4 | https://laws.lexinter.net/constitution/us/article-1/section-9/clause-4