The Justice Department is demanding that California take immediate steps to verify the citizenship of individuals identified by federal officials as potential noncitizen voters, escalating the Trump administration’s efforts to address suspected violations of federal election law.

In a Tuesday letter to California Secretary of State Shirley Weber, acting Deputy Attorney General Trent McCotter said the department had provided Los Angeles County officials with a password-protected thumb drive containing names of people the federal government believes are likely noncitizens who received mail ballots for the November election.

The state has 48 hours to determine whether any U.S. citizens were mistakenly included on the list. For individuals whose citizenship cannot be independently verified, the department instructed California to direct local election officials to set aside their mail ballots until their status can be determined. Officials were also told not to issue ballots to listed individuals who had not yet received them.

The letter warned that the federal government could seek emergency judicial relief if California fails to implement the requested process within the deadline.

“If you cannot implement this process by then, given the ongoing federal election, the United States will have no choice but to seek emergency relief,” McCotter wrote.

The Justice Department sent a separate letter containing similar demands to the Los Angeles County Registrar’s Office. Neither Weber’s office nor the county registrar immediately responded to requests for comment.

The dispute comes as the Trump administration has made identifying and prosecuting suspected noncitizen voting a priority. The department has charged approximately 90 people with various forms of election misconduct this year, including about 50 accused of voting as noncitizens.

Those cases represent a small share of the electorate. The United States had approximately 227 million registered voters during the 2024 presidential election, and noncitizen voting remains rare.

The latest confrontation follows a separate dispute over federal claims about noncitizen voter registrations. In July, Homeland Security Secretary Markwayne Mullin sent letters to California, Nevada, New Jersey and Pennsylvania alleging that as many as 250,000 noncitizens were registered to vote across those states.

Election officials questioned the reliability of the figures, including Weber, who challenged the federal government’s data.

“I have serious doubts about the reliability of your data and accuracy of your claims, since my office has not shared our statewide voter registration list with DHS or any other federal agency or official,” Weber said in response.

The latest letters place California and federal officials at odds over how to handle suspected noncitizen voters ahead of the midterm elections, with the Justice Department threatening court action if the state does not meet its deadline.