Schultz, a Republican, says the change is needed to reduce voter fraud, which he's made his key issue since taking office in 2011.
The rule allows Schultz's office to compare voter registration records against federal immigration lists. Anyone registered to vote flagged as a noncitizen is notified by mail that they may be unlawfully registered and should provide citizenship proof.
Opponents have unsuccessfully fought enactment of the rule. They say it intimidates immigrants who are citizens and may discourage them from voting.
The American Civil Liberties Union of Iowa says it will continue to fight the rule in court.