Section 2 of the 14th Amendment reads, in part, "... when the right to vote ... is denied to any of the male inhabitants of such State, being twenty-one years of age, and citizens of the United States, ... the basis of representation therein shall be reduced in the proportion which the number of such male citizens shall bear to the whole number of male citizens twenty-one years of age in such State."
Unfortunately, that provision is unenforcible. It would require drawing new districting maps and holding new elections. And in the meantime, the offending state could repeal the law in question.
However, there is a way to enforce it within my system for electing legislators. With multiple legislative votes per district, we an afford for some to go unused. I already proposed counting abstentions of registered voters, but now I want to count all the constitutionally eligible voters. When Republicans in a state government suppress the vote, the state as a whole would automatically, through the mechanics of the system, end up with less representation in Congress.
The power they lose would have been represented by Democrats, so they may not mind, but it does accomplish the original goal. However, I'd go further and use states' voting power in Congress as the basis of the number of electoral votes.