The US Justice Department has given California officials 48 hours to review a list of alleged noncitizen voters or face legal action, escalating a dispute over election procedures ahead of the November 3 elections.
The ultimatum, issued Tuesday in a letter reviewed by Reuters, demands restrictions on ballots associated with individuals whose citizenship remains unverified.
Acting Deputy Attorney General R. Trent McCotter addressed the letter to California Secretary of State Shirley Weber, stating that Los Angeles County officials had received a password-protected drive identifying individuals federal authorities believe may be noncitizens.
The department instructed California to withhold mail-in ballots from those listed until their citizenship is verified.
Ballots already distributed must be separated upon return, while previously submitted ballots should remain uncounted pending verification.
The letter warned that federal authorities could seek emergency judicial intervention if California fails to comply.
Justice Department spokeswoman Kiersten Pels confirmed the communication to Reuters and said the administration would pursue legal measures to enforce election laws.
California officials and the White House did not immediately comment.
The ultimatum follows months of federal pressure on states over alleged noncitizen voting, which multiple studies have found to be rare.
A September Reuters review identified more than 30,000 potential noncitizen voter registrations since 2000, potentially resulting from administrative errors, but found insufficient evidence establishing how many individuals actually voted.
In July, the Justice Department warned election officials nationwide about potential criminal liability for knowingly permitting unlawful voting.
It subsequently sued 30 states seeking access to voter records, losing 26 cases without securing a victory.
Federal authorities have also expanded investigations and prosecutions, announcing 16 criminal cases involving alleged illegal voting or fraudulent registration on Monday.
California's confrontation carries significant political implications as Republicans defend narrow congressional majorities.
The state recently approved a Democratic-favoring congressional map amid nationwide redistricting disputes.
Los Angeles voters will additionally consider allowing certain legally resident noncitizens to participate in municipal elections, further highlighting the distinction between local voting proposals and federal election eligibility.