Filed in federal court in Los Angeles, the lawsuit asks a judge either to bar the counting of ballots from the flagged voters or to require California to independently confirm their citizenship before tallying them. The dispute began after the federal government demanded access to a list of alleged noncitizen voters and urged state and Los Angeles County election officials to prevent those people from receiving ballots or having their votes counted until their status was checked.

The Justice Department’s filing says Homeland Security Investigations believes about 20,000 noncitizens are registered to vote in California. Federal officials previously put the figure at 190,000, a claim state officials have disputed. The lawsuit argues that sending ballots to people the government considers likely noncitizens has hindered federal efforts to investigate and enforce election laws.

Gov. Gavin Newsom called the lawsuit an attempt by President Donald Trump’s administration to suppress California voters and said the federal figures were fabricated. Secretary of State Shirley Weber rejected the demand, saying her office would not disenfranchise thousands of people on the basis of information or methods the federal government had not explained.

Weber said California works to keep voter rolls accurate and would review credible evidence of ineligible registrations. But she argued that the federal government’s requested steps were inconsistent with state and federal law. California’s voter rolls are maintained by the secretary of state and county election officials.

Attorney General Rob Bonta said the state would fight the case, accusing federal officials of promoting misinformation and questioning the timing of the suit. The Justice Department filed it shortly before California officials publicly declined the federal request.

The dispute comes amid broader scrutiny of the administration’s claims about noncitizen voter registration. Federal officials initially identified California and three other states as having more than 250,000 noncitizens registered collectively. In a separate review in Nevada, officials reduced an initial claim to 185 people; a subsequent review found all 185 were citizens.

A separate lawsuit filed earlier by the UCLA Voting Rights Project on behalf of the Coalition for Humane Immigrant Rights of Los Angeles and a Los Angeles resident seeks to prevent federal interference in California’s election administration. On Thursday, the coalition’s lawyers asked a judge for a temporary restraining order to stop the administration from pressuring state officials to withhold ballots. They argue the federal government lacks authority to direct California election officials and that flawed data could wrongly include naturalized citizens. The judge had not ruled on that request as of Thursday and directed the parties to confer and report back by Friday.

Matt Barreto, faculty director of the UCLA Voting Rights Project, said the federal government’s efforts conflict with constitutional provisions assigning states a role in administering elections and with the National Voter Registration Act. That law restricts major changes to voter rolls within 90 days of an election, according to the coalition’s argument.

The DOJ lawsuit also challenges aspects of California’s mail-ballot signature verification system. Republican-backed Proposition 39, which will appear on the ballot, would change signature verification and require voter identification if approved by a majority of voters.