The Department of Justice on Friday warned local election officials in California to cooperate with the administration to identify noncitizens on a list of registered voters or face potential legal action, according to a letter obtained by NBC News.

The department sent letters to 57 of California’s 58 counties in a move that signals an escalation in the Trump administration’s effort to prevent the state from counting ballots from voters the federal government identifies as likely noncitizens.

Los Angeles County received a similar letter last week.

NBC News obtained the letter sent to San Bernardino County Registrar of Voters Joani Finwall from the U.S. attorney’s office in Los Angeles. In it, First Assistant U.S. Attorney Bilal Essayli notes that his office is providing a list of 1,133 names of “likely aliens.”

“Within 48 hours, we ask that you commit to working with DOJ and DHS to identify who on the accompanying list is a citizen and who is not,” Essayli wrote. “I write to make unmistakably clear the legal implications of continuing to send vote-by-mail ballots to those people on the list or tabulating ballots cast by them until citizenship can be verified.”

For those whose citizenship status cannot be confirmed, Essayli asked the county to “immediately instruct the appropriate elections official to segregate — not cancel — those individuals’ vote-by-mail ballots until their citizenship status can be determined.”

“The legal consequences for either facilitating or ignoring federal crimes are significant. An alien voting in a federal election is a federal crime — and knowingly facilitating such conduct is equally unlawful,” Essayli wrote in the letter.

“The letters speak for themselves,” Essayli said in a statement to NBC News. “Any election official who knowingly processes the ballot of a noncitizen is opening themselves to legal jeopardy.”

The New York Times was the first to report the letters.

“Trump’s DOJ has not provided any evidence for their claims of massive voter fraud,” Sen. Alex Padilla, D-Calif., said in a statement late Friday. “They’ve admitted that the data they point to is inaccurate and unreliable. No matter how many lawsuits they file or how many election officials they threaten, they do not have the authority to interfere.”

The Trump administration has made the pursuit of noncitizen voters a priority in the run-up to the midterms and has singled out heavily Democratic California. The administration has sued to block the state from counting more than 20,000 mail-in ballots from voters it suspects are not U.S. citizens. On Thursday, it asked the 9th U.S. Circuit Court of Appeals to impose the restrictions before the lower court has ruled in the case.