A federal judge ordered the U.S. Border Patrol to stop conducting warrantless immigration stops across California's Central Valley on Tuesday, dealing a significant blow to the Trump administration's aggressive immigration enforcement tactics.

SACRAMENTO, United States, May 1 (Xinhua) -- A federal judge ordered the U.S. Border Patrol to stop conducting warrantless immigration stops across California's Central Valley on Tuesday, dealing a significant blow to the Trump administration's aggressive immigration enforcement tactics.

U.S. District Court Judge Jennifer L. Thurston issued a preliminary injunction that restricted Border Patrol agents from stopping people without reasonable suspicion or making arrests without a warrant unless they had probable cause that someone might flee.

"You just can't walk up to people with brown skin and say, 'Give me your papers,'" Thurston said during Monday's hearing, according to court documents obtained by CalMatters, a non-profit news website in California.

The American Civil Liberties Union, a leading civil rights organization in the United States, filed the lawsuit on behalf of United Farm Workers after agents from the El Centro Border Patrol sector conducted a three-day sweep called "Operation Return to Sender" in Kern County this January.

Agents detained farmworkers, day laborers and others at various locations, including a Home Depot parking lot and alongside highways.

Court testimony revealed troubling details about the operation. According to sworn declarations filed in court, agents slashed tires, physically removed people from vehicles, threw people to the ground, and used derogatory language toward farmworkers.

While Chief Patrol Agent Gregory Bovino claimed agents specifically targeted individuals with criminal and immigration histories, a CalMatters investigation revealed the agency had no criminal or immigration history on 77 of the 78 people arrested.

U.S. government attorneys argued the lawsuit was unnecessary because the agency had already begun retraining approximately 900 agents on Fourth Amendment requirements. However, when Judge Thurston asked how this training was conducted, government attorneys could not provide details.

The court also ordered Border Patrol to document every stop and provide reports within 60 days, despite government attorneys claiming this requirement would burden agents.

Elizabeth Strater, national vice president at the United Farm Workers, called the ruling significant but overdue. "It's not legal to snatch people off the street for looking like farmworkers or day laborers," she told reporters.

The injunction applies to the jurisdiction of the U.S. District Court for the Eastern District of California, including 34 counties, from the Oregon border to Bakersfield and from the coastal mountains to the Nevada border. It covers almost 8 million residents.

And the injunction will remain in effect while the case moves through the courts.

The California Central Valley, which covers about 51,800 square km, is a major agricultural region, supplying a significant portion of the nation's food and producing a wide variety of crops.

According to the U.S. Geological Survey, the Central Valley, using fewer than 1 percent of U.S. farmland, supplies 8 percent of U.S. agricultural output (by value) and produces 25 percent of the nation's food.

The California Farm Bureau said fears in the Central Valley have led to migrant farmworkers not showing up for work after the U.S. Border Patrol's crackdown in January, which had virtually halted the area's citrus harvest.