By REBECCA BOONE

A federal judge in California has barred Border Patrol agents from arresting someone suspected of living in the U.S. illegally unless they have a warrant or a reason to believe the person might flee before a warrant can be obtained.

Tuesday’s ruling from U.S. District Judge Jennifer L. Thurston also says Border Patrol agents can’t stop people without having reasonable suspicion or return them to their countries of origin via “voluntary departure” unless that person is informed of their rights and agrees to leave. The ruling only applies to people within the court’s Eastern District of California, Thurston said, where dozens of people were swept up in January after the Border Patrol launched an immigration enforcement action dubbed “Operation Return to Sender.”

The American Civil Liberties Union sued Department of Homeland Security Secretary Kristi Noem and U.S. Border Patrol officials on behalf of the labor union United Farm Workers and people who were targeted during the Border Patrol raids.

The ACLU said border patrol agents spent nearly a week unconstitutionally detaining people who “appeared to be farmworkers or day laborers, regardless of their actual immigration status or individual circumstances.” The detainees were bussed to the border, held without any way to contact family or attorneys, and coerced into signing papers that said they had waived their right to see an immigration judge and voluntarily agreed to leave the country, the ACLU said.

“The evidence before the Court is that Border Patrol agents under DHS authority engaged in conduct that violated well-established constitutional rights,” Thurston wrote. She said the Border Patrol would have to provide a report showing exactly who is detained or arrested without warrants, and why, every 60 days until the lawsuit is concluded.

Attorneys for the Border Patrol had argued the judge lacked jurisdiction to consider the case, because federal law says that immigration matters can generally only be appealed once an immigration judge has issued a final order. Besides, the government’s attorneys said, the lawsuit is moot because the U.S. Border Patrol has already issued new guidance and training to its agents detailing exactly when people may be stopped or arrested without warrants, and what rights detainees have after their arrest.

But Thurston said the Border Patrol can’t claim the lawsuit is moot simply because it issued a new policy after it was sued. The language in the new policy isn’t strong enough to guard against the illegal stops, Thurston said, and there is no reason to believe that the policy wouldn’t be changed again in the future.