In letters sent Tuesday to Secretary of State Shirley Weber and Los Angeles County Registrar of Voters Dean Logan, acting Deputy Attorney General Trent McCotter asked officials to confirm the citizenship of voters whose names were provided on a password-protected thumb drive. For voters whose status could not be independently confirmed, McCotter asked officials to set aside — but not cancel — their mail ballots until eligibility could be determined.

The demand arrived as California counties had begun mailing ballots. Most counties started sending them the previous week, according to state officials cited in the correspondence.

California Attorney General Rob Bonta denounced the administration’s action Wednesday, accusing President Donald Trump of promoting unfounded concerns about voter fraud and intimidating voters during an ongoing election. Bonta questioned the credibility of the administration’s claims, saying it had “zero credibility.”

The Justice Department warned that it would seek emergency court relief if state officials did not meet the 48-hour deadline. The letters did not establish that the voters identified by the federal government were noncitizens; they described them as people the department believed were likely noncitizens.

Logan said Los Angeles County officials did not attempt to open the thumb drive because it failed to meet the registrar’s security standards. Weber’s office had not responded to a request for comment by Wednesday.

David Becker, a former federal prosecutor who leads the Center for Election Innovation and Research, questioned the timing. He said California’s voter lists are public and argued that the federal government had had ample time to review them before ballots went out. Becker also raised concerns about the department’s decision to act close to Election Day, when federal election investigations are generally subject to restrictions.

It was not clear whether other California counties received similar demands. Election officials in Marin, Sonoma, Contra Costa, Solano and Yolo counties said they had not received federal communications seeking citizenship proof for voters on their rolls.

Sonoma County Deputy Chief Registrar Wendy Hudson said the county would make no changes to its vote-by-mail procedures unless directed otherwise by the secretary of state. She said registration information is checked against state and federal records and that applications are not processed if applicants do not confirm they are U.S. citizens.