Naturalized citizens have sued Iowa Secretary of State Paul Pate and other election officials after he instructed them to challenge the ballots of over 2,000 voters.

Last week, Pate’s office said that it gave county auditors a list of 2,022 people who told the state’s Department of Transportation that they were not citizens but later registered to vote or voted.

Since those voters may have become naturalized citizens in the time between telling the Transportation Department that they were not citizens and participating in the U.S. election process, Pate’s office told county auditors to challenge their ballots and have them cast a provisional ballot instead.

The voters would have seven days to show proof of citizenship before their ballot is counted.

ACLU Challenges Election Officials

The American Civil Liberties Union (ACLU) of Iowa filed a lawsuit against Pate and five election auditors in federal court late Wednesday on behalf of four voters flagged by Pate as registered voters who might not be citizens and the League of United Latin American Citizens of Iowa (LULAC).

According to the complaint, the four voters are naturalized citizens, one of whom registered last year, a day after he became a citizen.

“Yet he was placed on the Secretary’s covert list and wrongfully subjected to investigation and an election challenge for following the law and exercising his right to vote,” the complaint states.

The lawsuit alleges that Iowa election officials are burdening the right to vote and discriminating against naturalized citizens. Officials are treating this group of voters differently from others in violation of their constitutional right to equal protection, the suit claims.

The suit asks for the Transportation Department list to be revoked and for voters on it to not be challenged on this basis.

Pate in a ‘Balancing’ Act

Pate told reporters Wednesday, before the lawsuit was filed, that the Transportation Department list is the “only list that we have available to us” without access to federal immigration records.

“We’re balancing this process. We want everyone to be able to vote. That’s why none of them have been taken off the voter rolls,” Pate said.

However, he added, “We do owe an obligation to make sure that they are citizens now.”

Republicans have made non-citizen voting a big issue ahead of the November 5 election. Despite it already being illegal for non-citizens to register to vote or to vote in federal elections, the Republican-led House voted to pass the Safeguard American Voter Eligibility (SAVE) Act in July, which would require those registering to vote to provide documentary proof of U.S. citizenship. The bill remains in the House.

While there is no evidence that non-citizen voting is occurring in significant numbers, Iowa and some other states have identified dozens of such cases.

‘We Will Defend Our Election Integrity’

Before the lawsuit was filed, Iowa Attorney General Brenna Bird said Wednesday that the U.S. Department of Justice “called the State in an attempt to pressure Iowa into letting noncitizens vote.”

“Every legal vote must count and not be canceled by an illegal vote,” she said. “In Iowa, we will defend our election integrity laws and protect the vote.”

A Justice Department spokesperson declined to comment to the Associated Press (AP).

The AP also reached out to Pate and Bird on Thursday for comment on the lawsuit.

This article includes reporting from The Associated Press.