A federal judge in California is putting limits on pre-election field operations conducted by the Department of Homeland Security that the agency says is aimed at trying to find noncitizens who have illegally voted in nine states.

In recent weeks, armed Homeland Security Investigations officers have carried out field operations and visited homes to interview people suspected of illegally voting as noncitizens. The targets can include people who became citizens but voted before they naturalized.

In a 19-page order late Wednesday, U.S. District Judge Araceli Martínez-Olguín, an appointee of President Joe Biden, wrote that the federal government was using "flawed" data in the initiative and that its efforts likely violated the Voting Rights Act, which bars voter intimidation.

Martínez-Olguín referenced a disclosure last month from a U.S. Citizenship and Immigration Services whistleblower that alleged rushed efforts to match data to create a target list of potential noncitizens on voter rolls, and that the list includes U.S. citizens. She also pointed to HSI's social media posts, including one that showed agents handcuffing a California man accused of unlawfully registering to vote.

The judge wrote that the government's use of unreliable and incomplete data along with highly publicized arrests "lead to an objectively reasonable fear of law enforcement entanglements that intimidates citizens from urging or aiding others in exercising their right to vote." HSI field operations were planned in California, Connecticut, Georgia, Missouri, Nevada, New York, Pennsylvania, Washington and Wisconsin, according to documents produced in the case and CNN reporting.

Martínez-Olguín barred DHS officers in those states from conducting field operations targeting people they "know, suspect, or should reasonably know or suspect are U.S. citizens," or that are based "wholly" on USCIS matching data without further investigation.

In a declaration, USCIS official Nicolas Bartell had told the judge his team manually reviews records before referring them to HSI, but acknowledged the "low possibility" citizens could be "erroneously identified as potential aliens" in federal records. He wrote the risks were mitigated by safeguards his office takes "and any remaining risks were outweighed by the need to support the agency's law-enforcement and election-integrity mission."

It's unclear how much of an effect the judge's order will have on the federal government's highly publicized campaign to find noncitizen voters. States reviews and audits have consistently found voting by noncitizens to be extremely rare.

"DHS is laser focused on identifying, prosecuting, and removing aliens who vote and dilute the votes of U.S. citizens. ONLY Americans should elect American leaders," the agency wrote in a statement. "We have no plans to question or investigate people we believe to be U.S. citizens." The order is set to take effect on Friday and would be in effect through election night, though the federal government could appeal.

The judge's ruling came in a lawsuit filed last month by a coalition that includes San Francisco and Santa Clara counties, the city of San Francisco, nursing unions and Voto Latino Foundation. Protect Democracy and the National Immigration Law Center are litigating the case against the Department of Homeland Security and the Department of Justice.

"Today, the courts affirmed a vital principle of our democracy: Voting is a fundamental right that citizens — whether born here or naturalized — should be able to exercise without armed government agents harassing them," Beau Tremitiere, a lawyer with Protect Democracy, said in a statement.

"It was clear from the start that DHS built its lists on bad data, never checked how often it was wrong, and recklessly sent agents to people's homes weeks before an election," he added.

A court filing by the California Nurses Association and National Nurses United described naturalized citizen members who no longer wanted to attend political rallies, sign up to be election poll workers, or vote in person because of the federal operations.

The order comes as the Department of Justice is suing California and demanding the state segregate 20,000 ballots from people federal officials say they believe are "likely" noncitizens.

A preliminary review of a sample of that list by Los Angeles County election officials found many of the registrations were canceled, inactive or had no voting history, and some pertained to people who indicated they were born in the U.S.

The DOJ announced charges against 28 green card holders across the state on Monday who are accused of illegally voting or registering to vote.