Federal prosecutors sent letters to county registrars across California on Friday demanding that local officials set aside and verify ballots that the Department of Justice said may belong to noncitizens, according to the Los Angeles county registrar and a letter obtained by the Associated Press.The letters are the latest escalation in a legal battle between California and Donald Trump’s Department of Justice, which has recently focused on the state in its efforts to root out noncitizen voting ahead of the midterm elections.Data shows illegal voting by people who are not US citizens is incredibly rare, difficult to prove and has not been shown to change the outcome of races.Earlier this month, the federal government targeted Los Angeles county and the California secretary of state’s office in a lawsuit that aimed to block them from counting the votes of roughly 20,000 people who are “likely” noncitizen voters. A hearing on the case is scheduled for Tuesday.The Trump administration asked the ninth circuit court of appeals to rule on the lawsuit barring a decision from the district judge assigned to the case.

They set a deadline for Saturday.Now, according to the LA county registrar’s office, at least 18 counties across the state have received similar letters.They have been given a 48-hour deadline to provide identifying information corresponding with ballots that the federal government believes were sent to noncitizens illegally registered to vote. The letter requests that county officials also sequester any ballots where citizenship cannot be verified.“Any election official who knowingly processes the ballot of a noncitizen is opening themselves to legal jeopardy,” said first assistant US attorney Bill Essayli.The justice department is asking counties to send information about the voters it suspects are noncitizens including social security numbers, ID information, a copy of their registration and more.That information can help the government and state quickly assess each person suspected of illegally registering to vote, said the letter sent to San Bernardino County voting officials.

The letter says the government’s list of suspected noncitizen voters includes 1,133 people from the inland southern California county.California’s secretary of state and the Los Angeles county registrar have opposed the federal government’s demands. In legal filings, lawyers for California say the request threatens to delay the certification of the vote and undermine the legitimacy of the November midterms.

They have also argued that the federal government’s data is unreliable and that their demands risk disenfranchisement of citizens.Voting is under way in California, with the state’s more than 23 million registered voters receiving ballots in the mail earlier this month. The state said in legal filings that over 330,000 mail-in ballots have already been counted.The letters on Friday came on the heels of statewide sweep by federal authorities earlier in the week, where 28 people from the list of 20,000 were charged with illegally registering to vote.

Some were also charged with illegally voting and lying on naturalization paperwork. Those charges could lead to years in prison.