U.S. District Judge Araceli Martínez-Olguín’s order applies to planned operations in California, Connecticut, Georgia, Missouri, Nevada, New York, Pennsylvania, Washington and Wisconsin. It bars DHS officers from conducting field operations against people they know, suspect or reasonably should suspect are U.S. citizens. Officers also may not base operations entirely on data matches from U.S. Citizenship and Immigration Services without further investigation.

The order is scheduled to take effect Friday and last through election night. The federal government could appeal, and the extent to which the restrictions will alter the campaign remains uncertain.

In a 19-page ruling issued Wednesday, Martínez-Olguín said the government’s reliance on unreliable and incomplete records, alongside publicized arrests, could cause people to fear encounters with law enforcement. That fear, she wrote, could deter citizens from helping others exercise their voting rights.

Homeland Security Investigations officers have recently visited homes to question people suspected of voting illegally. Some targets may have become U.S. citizens after the elections in question, meaning they were citizens when investigated even if they were not citizens when they voted.

The judge cited a whistleblower’s account alleging that federal officials rushed to match records to create a list of potential noncitizens on voter rolls, which included U.S. citizens. She also referenced HSI social media posts, including one showing agents handcuffing a California man accused of unlawfully registering to vote.

USCIS official Nicolas Bartell told the court that staff manually review records before referring them to HSI. He acknowledged a low possibility that citizens could be mistakenly identified as potential noncitizens, but said safeguards reduced the risk and that remaining risks were outweighed by law-enforcement and election-integrity goals.

DHS said it has no plans to question or investigate people it believes are U.S. citizens, and said its focus is on identifying and prosecuting noncitizens who vote. State reviews and audits have consistently found noncitizen voting to be extremely rare.

The lawsuit was brought by a coalition that includes San Francisco and Santa Clara counties, the city of San Francisco, nursing unions and Voto Latino Foundation. The California Nurses Association and National Nurses United told the court that some naturalized-citizen members had become reluctant to attend political rallies, volunteer as poll workers or vote in person because of the federal operations.

The ruling comes amid a broader dispute over voter-roll investigations. The Justice Department is suing California and seeking to have 20,000 ballots segregated based on federal officials’ claims that voters are likely noncitizens. A preliminary county review found that many people on the list had canceled or inactive registrations or no voting history; some records were for people who said they were born in the United States.