US Constitution Series, Amendment XXIV

Amendment XXIV. Abolition of the Poll Tax Qualification in Federal Elections

SEC. 1. The right of citizens of the United States to vote in any primary or other election for President or Vice President, for electors for President or Vice President, or for Senator or Representative in Congress, shall not be denied or abridged by the United States or any State by reason of failure to pay any poll tax or other tax.

SEC. 2. The Congress shall have power to enforce this article by appropriate legislation.

The poll tax was used to prevent poor blacks (and other poor people) from voting.