The administration has insisted that immigrants voting is a major problem nationwide, when in fact it is quite rare, as even its own investigations have shown.

Trump has been criticized in the past for voting by mail despite his long history of railing against that method of submitting ballots.

Marva Cook was adopted as a toddler and had always assumed she was a U.S. citizen, she told Homeland Security investigators earlier this month, according to the criminal complaint.

The letters are the latest escalation in a legal battle between California and President 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.

Election officials across the state received letters from the agency saying if they fail to comply, they “risk significant federal scrutiny.”

© Philip Cheung for The New York Times

Most of the immigrants targeted by federal authorities in California this week for alleged voter fraud had applied for U.S. citizenship and now face charges related to lying on forms or during interviews. Those charges could lead to years in prison and thwart their efforts to naturalize.

The diverse, multifaith group is training all the way through the end of October online and in person learning de-escalation techniques and equipping themselves with knowledge of local laws and resources.

The Trump administration is escalating its fight with California ahead of next month's midterm election, warning that local officials who process and tabulate ballots submitted by suspected noncitizen voters are putting themselves at risk of criminal investigation and potential prosecution.