Election officials in two Northern California counties say they received grand jury subpoenas tied to alleged noncitizen voting in the final days before Tuesday's midterm election, marking a sharp escalation in the Justice Department's confrontation with the state over its voter rolls.

Officials in Santa Clara and Sonoma counties told CBS News that each jurisdiction was served with a subpoena issued by a grand jury at the request of federal prosecutors in the U.S. Attorney's Office for the Northern District of California. The subpoenas were first reported by Bloomberg Law. CBS News has reached out to the Justice Department for comment.

The demands are the latest step in a federal pressure campaign to get California to set aside some 20,000 mail ballots the department claims were sent to suspected noncitizens ahead of the election. State and local officials have refused, questioning the accuracy of the federal government's list and warning that segregating the ballots could disenfranchise legitimate voters. The department's civil lawsuit seeking ballot segregation failed in court, with multiple federal judges, up to and including the U.S. Supreme Court, refusing to force counties to take that step.

Even so, the Justice Department has pressed ahead with parallel criminal investigations that appear to have widened in recent weeks, reaching beyond individual noncitizens who may have voted in past elections to scrutinize the conduct of state and local election officials themselves.

Two weeks before the midterms, officials in Los Angeles County were served with similar demands seeking copies of their communications with federal officials concerning noncitizen voting, along with records detailing the county's procedures for identifying and screening noncitizens out of the voter rolls. The response deadline had been set for Wednesday, Nov. 4, but a spokesperson for the Los Angeles Registrar-Recorder/County Clerk said it has since been extended by a few weeks.

A Sonoma County spokesperson said the subpoena delivered there on Saturday seeks information about a specific individual the department alleges may have voted in prior elections, as well as records showing how the county responded to demands that it isolate ballots cast by suspected noncitizens. A person familiar with the Santa Clara subpoena said it made similar requests, and that both appeared to probe whether the counties had complied with the segregation demands even after the courts declined to require it.

Sonoma County counsel Joshua Myers pushed back in a statement. "The Sonoma County Registrar of Voters is committed to conducting fair, transparent elections in full compliance with the law while preserving access for all eligible voters," he said. "We have consistently maintained that there is no legal basis for the federal government's requests for Sonoma County to segregate ballots." Doing so, Myers added, "would violate several laws that ensure the safe and lawful administration of our elections."

Tony LoPresti, counsel to Santa Clara County, struck a similar tone. "We have been steadfast in our position that there's no legal basis for the federal government's attempts to intervene in the elections process," he said in a statement. Both lawyers said they are still evaluating the Justice Department's document demands.

It is not the first time Santa Clara County has faced such a subpoena. A spokesperson for its Registrar of Voters said the office received two subpoenas in early September, both requesting specific voter information, and that other counties received similar requests around that time. Federal prosecutors in California have since filed criminal charges against people they allege may have unlawfully voted in prior elections.

Two sources briefed on the matter told CBS News that senior Justice Department leaders in Washington ordered California's four U.S. attorneys to issue the recent flurry of subpoenas to county officials or else face termination. In the days before the election, a federal judge ordered the department to stop issuing threats to state and local election officials, but the U.S. Court of Appeals for the Ninth Circuit later lifted that order.