Approximately 5% of Arizona voters will need to confirm their proof of citizenship with the state following a decadeslong error. 

Arizona counties have slowly begun sending letters to thousands of longtime voters, instructing them to provide documentation proving their citizenship before they vote again, according to a report from VoteBeat. Around 200,000 longtime residents are set to receive these letters after they were inadvertently caught up in a statewide error that did not track voters’ proof of citizenship.