U.S. District Judge Araceli Martínez-Olguín issued a preliminary injunction late Wednesday, finding that the interviews could violate the federal Voting Rights Act. She also raised concerns about the government’s use of flawed and incomplete information to identify people for questioning.

The case was brought by voter and immigrant-rights advocates, joined by the city and county of San Francisco and Santa Clara County. The plaintiffs argued that armed agents questioning voters at their homes could discourage eligible people from voting.

Homeland Security Investigations has stepped up field investigations in nine states, including California. The federal government has said the investigations target people it suspects registered to vote illegally.

Martínez-Olguín wrote that the government relied on “admittedly flawed and incomplete data” to prepare a list of people for interviews in the months before the election. She also cited a social media campaign featuring images and videos of people being arrested.

The federal government has used the same data in other actions involving California elections. The Justice Department charged 28 California green-card holders with election offenses on Monday, according to the case information cited in the ruling. Last week, the government sued California and Los Angeles County over voter rolls after demanding proof of citizenship for about 20,000 registered voters it believes may be noncitizens.

Beau Tremitiere, an attorney with the Protect Democracy Project who argued for the plaintiffs, said the ruling affirmed that citizens should be able to vote without “armed government agents harassing them.”