22 CFR 40.104: Unlawful voters.

(a) Subject to paragraph (b) of this section, an alien is ineligible for a visa if the alien has voted in violation of any Federal, State, or local constitutional provision, statute, ordinance, or regulation.

(b) Such alien shall not be considered to be ineligible under paragraph (a) of this section if each natural parent of the alien (or, in the case of an adopted alien, each adoptive parent of the alien) is or was a citizen (whether by birth or naturalization), the alien permanently resided in the United States prior to attaining the age of 16, and the alien reasonably believed at the time of such violation that he or she was a citizen.