Local election officials across California are confused and frustrated after receiving letters from President Donald Trump’s Justice Department demanding that county registrars sequester ballots that the federal government believes were sent to noncitizen voters ahead of the midterm elections.

The letters, which were sent on Friday, ask for sensitive information, including Social Security numbers, on roughly 20,000 voters. It is illegal for noncitizens to register to vote or cast a ballot. 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.

“All of this is simply meant to raise huge doubts about the integrity of this election,” said John Tuteur, the registrar of voters for Napa County in California’s wine country.