A federal judge in Los Angeles is set to hear arguments over whether the Department of Justice can bar California from counting the ballots of of some 20,000 people until it can confirm they are U.S. citizens.

SAFIYAH RIDDLE The hearing before U.S. District Judge David O. Carter comes as voting is underway statewide with a week left before the midterm election concludes Nov. 3. Noncitizen voting has been a key focus of President Donald Trump’s administration as U.S. voters decide which party will control Congress for the rest of his term, though available data indicates the illicit practice is exceedingly rare The Republican administration sued election officials in the heavily Democratic state in mid-October, accusing them of failing to meet a 48-hour deadline to review a list of 20,000 names it alleged were likely noncitizens on the state’s voter rolls. The federal government is asking Carter to block the state from counting those ballots until the voters’ immigration status can be verified.

The federal government had sought an emergency appeals court ruling before Tuesday’s hearing but was rebuffed by a divided panel of the 9th U.S. Circuit Court of Appeals.

California officials say the lawsuit came too late California officials warned in court filings that any effort to heed the Trump administration’s requests would potentially “disenfranchise legitimate voters,” delay certification of the election and “cause general uncertainty in the election results.”Two of the three appeals panel judges echoed those concerns after hearing oral arguments Sunday. While the ruling mainly called it premature for an appeals court to get involved before the district court could hear the case, the two judges wrote separate concurrences making it clear they wouldn’t support setting aside the ballots.

The dissenting judge argued, however, that both state and federal law bar noncitizens from voting and that compels California to vet potentially illegal ballots before they are counted. The failure to do so, he wrote, would cause irreparable harm to the election.

California mails ballots to all active registered voters among the state’s roughly 23 million electorate. More than 3 million voters statewide have already cast ballots.

At least one county registrar, Clinton Curtis in Shasta County, testified in a sworn declaration submitted by the federal government that setting apart ballots flagged by the Justice Department would be feasible.

“In my experience, locating and segregating challenged ballots is entirely possible and not catastrophic,” Curtis wrote. But local elections officials offered conflicting testimony in which they described serious obstacles.

Assistant Registrar-Recorder Monica Flores argued in court filings that it would be impossible to set apart votes for immigration status verification once they’ve been counted.

Voting information is confidential, she said in the filing, noting that once a ballot is mailed in, it is separated from its envelope with its individual voter identification markings, making it impossible to verify based on information provided by the federal government.

State and federal government battle over accuracy of list At the heart of the dispute is whether the Justice Department’s list is accurate in the first place.

Flores also wrote that her staff went through a sample of 200 records from the Trump administration’s list. They found the sample included canceled or inactive registrations, individuals with no voting history and voters who appeared to have been born in the U.S., which the filing notes “is strong evidence of citizenship.”Nicolas Bartell, the associate director of the federal Fraud Detection and National Security Directorate, said his department re-checked those 200 records and found that only four likely had citizenship and one person was dead.

The directorate is a specialized division within U.S. Citizenship and Immigration Services. Elsewhere in the filing, Bartell said the investigation was “ongoing” and noted that at least 189 records have “minor data discrepancies” -- but he didn’t say whether those records overlapped with Los Angeles’ sample.

Bartell in a separate filing gave the most detailed account yet into its methodology for developing the 20,000 names in a court filing on Monday. Notably, the federal government is not using the SAVE database, which judges elsewhere have ruled illegally aggregates sensitive personal data and risks purging eligible voters from the rolls.

Bartell wrote that the agency cross referenced publicly available voter registration data with a combination of data from a third-party data collection site, Department of State records and Social Security Administration records. Then, an individual agent combs through the list of registered voters whose citizenship could not be verified using government data.