The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude.
— from the 15th Amendment
How do you think Southern states got around this amendment?
Until the 1950s and 60s poll taxes were put in place in southern US states, preventing poor farm workers and African Americans from voting because they could not afford to pax the poll tax.