The US ​Justice Department on Tuesday gave California officials 48 hours to review a list of alleged noncitizen voters or face legal action, according to ‌a letter reviewed by Reuters - part of an unprecedented effort to find evidence of voter fraud ahead of next month's elections.

The letter, written by acting Deputy Attorney General R. Trent McCotter and addressed to California Secretary of State Shirley Weber, says the Justice Department provided officials in Los Angeles County with a "password-protected thumb drive" with the names of people the federal government "believes are likely noncitizens" and ​were sent mail-in ballots.

The letter demands that the state refuse to send ballots to those on the list until their citizenship status has been confirmed. Voters ​in question who have already received ballots should have their ballot "segregated" once it is mailed back; ballots already returned should not ⁠be tabulated "until citizenship has been determined," the letter stipulates.