California says the move to block ballots from suspected noncitizens could disenfranchise eligible voters.

The administration of United States President Donald Trump has asked the Supreme Court to stop California from counting mail-in ballots from more than 20,000 voters it claims are not US citizens.

The emergency request, filed on Monday, just one day before the midterm elections, is the latest development in a legal battle between the administration and California, a Democratic stronghold and the most populous US state.

California says the move could disenfranchise thousands of eligible voters.

The Department of Justice wants California to set aside ballots from voters on a list compiled by the Department of Homeland Security until after their citizenship status is confirmed.

But California says the list is unreliable and could include thousands of US citizens.

Voting has been under way since early October, and state officials say it would be nearly impossible to separate the ballots in question.

Last week, a federal judge rejected the administration’s request, raising concerns about the reliability of the data on the list.

“If the executive can discount votes and threaten an ongoing election due to unproven allegations, then our democracy is in danger,” Judge David Carter wrote.

The administration has turned to the Supreme Court after a federal appeals court also rejected the request on Friday.

The dispute comes as Republicans fight to retain control of Congress in Tuesday’s elections.

Trump has repeatedly made false claims about widespread voter fraud, but studies and state audits have shown that ineligible voting, including by noncitizens, is rare.