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Texas Attorney General Ken Paxton sued the Biden administration on Tuesday, accusing the federal government of failing to help Texas check the citizenship status of some of the state’s registered voters — even as Paxton conceded that noncitizen voting is illegal and extremely rare.

In the lawsuit, Paxton argued that the federal government is required to assist states in verifying the citizenship status of registered voters, and he accused the U.S. Department of Homeland Security of failing to do so.

The lawsuit escalates Paxton’s hunt for noncitizen voters just two weeks before the election and a day after early voting began in Texas. He has pressed Texas Secretary of State Jane Nelson to request that the federal government hand over data the state could use to cross-check its voter rolls.

U.S. Citizenship and Immigration Services on Oct. 10 pointed Nelson to a program it maintains that states may use to verify individuals’ naturalized or acquired citizenship status. Immigration officials have gone back and forth with officials in several states over the data it can provide.

“The Systematic Alien Verification for Entitlements (SAVE) program is the most secure and efficient way to reliably verify an individual’s citizenship or immigration status, including for verification regarding voter registration and/or voter list maintenance,” the agency’s director, Ur M. Jaddou, wrote to Nelson, adding that the agency “currently cannot offer an alternative process to any state.”

The lawsuit, meanwhile, argued that the program is “not an adequate tool, on its own, for a state seeking to verify the citizenship status of an individual on the voter rolls.”

The Department of Homeland Security did not immediately respond to a request for comment.

Paxton, along with Republicans around the country led by former President Donald Trump, have repeatedly raised and used unsubstantiated concerns about noncitizen voting to cast doubt on the integrity of the election.

Noncitizen voting is illegal under both federal and state law. Experts say noncitizen voting is exceedingly rare, and that there is no evidence it affects election outcomes.

In an Oct. 7 letter to USCIS requesting citizenship data, Paxton acknowledged that the vast majority of individuals whose citizenship status his office was looking to confirm were eligible and lawful voters.

On Oct. 2, Paxton demanded Nelson’s office provide him with a list of possible noncitizens who are registered to vote.

Nelson then shared the voter records for anyone who does not have a Texas driver’s license or identification card number on file in its statewide voter registration system. She warned explicitly that the records “do not reflect, and are in no way indicative of, a list of potential non-United States citizens on the State’s voter rolls.”

Still, Paxton suggested that the state had “no way of knowing” whether any registered voters were in fact noncitizens and thus ineligible.

“The Biden-Harris Administration has refused to comply with federal law, presenting yet another obstacle for Texas to overcome in ensuring free and fair elections in our state,” Paxton said on Tuesday.

Democrats, meanwhile, have criticized the state GOP’s public crackdown on noncitizen voting as voter intimidation that could suppress eligible voters and undermine public confidence in election results.

In late August, Gov. Greg Abbott boasted that the state had removed more than 1 million ineligible voters from its rolls, including 6,500 noncitizens — boosting unsubstantiated Republican claims that noncitizens are planning to vote en masse to swing the election toward Democrats.

A Texas Tribune and ProPublica investigation found that Abbott’s claims about noncitizens on the voter rolls were almost certainly inflated, and in some cases, wrong.

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