FILE PHOTO: National Guard troops wear gas masks during protests against federal immigration sweeps, in Los Angeles, California, U.S., June 12, 2025. REUTERS/David Swanson/File Photo

By Dietrich Knauth and Tom Hals

(Reuters) -A federal judge on Tuesday blocked U.S. President Donald Trump's administration from using the military to fight crime in California, as the Republican president threatens to send troops to more U.S. cities including Chicago.

San Francisco-based U.S. District Judge Charles Breyer found that the Trump administration willfully violated a law known as the Posse Comitatus Act, which sharply limits the use of the military for domestic enforcement, by employing troops to control crowds and bolster federal agents during immigration and drug raids. The administration deployed 4,000 National Guard and 700 active duty U.S. Marines to Los Angeles in June.

Tuesday's ruling dealt a setback to Trump's push to broaden the role of the military on U.S. soil, which critics say is a dangerous expansion of executive authority that could spark tensions between troops and ordinary citizens.

Breyer put the ruling on hold until September 12. The Trump administration is likely to appeal.

Trump said at a news conference that the Los Angeles deployment restored order and he intended to send the military to more cities.

"Chicago is a hellhole right now. Baltimore is a hellhole right now," Trump said. "We have the right to do it because I have an obligation to protect this country."

The injunction applies only to the military in California, not nationally. But the judge said that Trump's stated desire to send troops to Chicago and other cities meant that an injunction was necessary to prevent future violations of the law that separates the military from law enforcement.

Trump has said the troops were needed in Los Angeles to protect federal agents carrying out immigration enforcement, after large-scale immigration raids triggered protests. Lawyers for the Trump administration had argued that the U.S. Constitution permits presidents to use troops to protect federal personnel and property as an exception to the Posse Comitatus Act.

"There is no question that federal personnel should be able to perform their jobs without fearing for their safety," wrote Breyer, who was nominated to the bench by Democratic President Bill Clinton and is the brother of former Supreme Court Justice Stephen Breyer.

"But to use this as a hook to send military troops alongside federal agents wherever they go proves too much and would frustrate the very purpose of the Posse Comitatus Act," Breyer said.

The Los Angeles deployment drew wide condemnation from Democrats, who said Trump was using the military to stifle opposition to his hardline immigration policies.

"The people of California won much needed accountability against Trump's ILLEGAL militarization of an American city!" California Governor Gavin Newsom, a prominent Democrat who brought the lawsuit, wrote on X on Tuesday.

Around 300 National Guard remain in Los Angeles, although protests have long died down, and the administration has extended their deployment into November.

California said in a Monday court filing that those remaining troops should be returned to the state's control.

The state said that the continued presence of troops could interfere with California elections in November by intimidating voters and "chilling participation."

California had challenged Trump's decision to take control of the state's National Guard in June, but it lost that fight on appeal. The state said on Monday that circumstances had changed and the decision to extend the troop deployment was not legally justified.

Breyer's ruling does not bind other judges but could shape how other courts interpret the law, which has rarely been addressed by the courts.

"It's going to be highly influential for any challenges in other cities," said Brenner Fissell, a professor at Villanova University Charles Widger School of Law. "If a judge doesn't agree with this, he's going to or she's going to have to explain why."

Trump has also deployed the National Guard to Washington, D.C., a federal district where Trump wields exceptional power.

(Reporting by Tom Hals in Wilmington, Delaware and Dietrich Knauth in New York; Additional reporting by Jonathan Stempel and Jack Queen in New York; writing by Susan Heavey and Luc Cohen, Editing by Rosalba O'Brien and Noeleen Walder)