But when the right to vote at any election ... is denied to any of the male inhabitants of such State ... 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.
I've abridged Section 2 but this is the gist.
I know that denial occurred for 100 years (at least) after passage of the amendment but I'm wondering if Congress ever reduced a state's representation due to denying citizens the right to vote.