Washington — The Justice Department sued California on Thursday, alleging that the federal government has identified more than 20,000 noncitizens who are unlawfully registered to vote.

The lawsuit, filed in the U.S. District Court for the Central District of California, came after Acting Deputy Attorney General Trent McCotter sent letters to counties earlier this week, including Los Angeles, ordering them to review a list of names of suspected noncitizens who he alleged received mail-in ballots for the upcoming midterm elections. 

“State-facilitated voter fraud is unacceptable in the United States of America,” Attorney General Todd Blanche said in a statement announcing the lawsuit.

“If found responsible in a court of law, the State of California will have seriously undermined confidence in our electoral system and violated laws that protect our nation’s representative system of government.”

In the letter that McCotter sent to the Los Angeles County Registrar-Recorder/County Clerk, he enclosed a password-protected thumb drive that he said contained names compiled by the Department of Homeland Security, and imposed a 48-hour deadline for the clerk’s office to review the list.

Dean Logan, the registrar-recorder and clerk, said in a statement responding to McCotter’s demands that the county would not be reviewing the materials on the thumb drive because doing so would conflict with “established data privacy and information security protocols.” He said the device was not considered a “secure medium.”

Secretary of State Shirley Weber, meanwhile, said the Justice Department had not provided the list of names and blasted the Trump administration for what it said were “unsubstantiated claims” that California had 190,000 noncitizens on its voter rolls.

In Thursday’s lawsuit, the Justice Department accused the state of failing to work with the federal government to correct the alleged problems with its voter rolls.

“The Federal Government asked California to work collaboratively to identify any noncitizens registered to vote in the State. California made no serious effort to do so,” the lawsuit said. 

“The United States thus seeks commonplace election relief when a ballot is called into question. This Court should enjoin California from presently tabulating vote-by-mail ballots from likely noncitizens in the upcoming federal election until the voter’s citizenship status can be determined,” it added.

CBS News has reached out to the secretary of state and the Los Angeles County Registrar-Recorder/County Clerk for comment.

The Justice Department’s Civil Rights Division has filed 31 lawsuits in an effort to force states to hand over unredacted copies of their voter rolls. The division has said it wants to ensure states are keeping clean voter lists, but it has since acknowledged that it also intends to share the data with the Department of Homeland Security so that the lists can be screened for noncitizens.

Harmeet Dhillon, the assistant attorney general for the Civil Rights Division, sent letters to all 50 states in July threatening to take criminal action if they knowingly allowed noncitizens to remain on their voter rolls.

So far, the Justice Department has lost 26 of those cases, and has not achieved one legal victory to date. 

It has resorted to using publicly available voter lists and other investigative means to try to identify noncitizens who may be registered in those states.