A federal judge has blocked former U.S. President Donald Trump’s deployment of National Guard troops and Marines in California, ruling that the move violated long-standing restrictions on military involvement in domestic law enforcement.

U.S. District Judge Charles Breyer said the deployment to Los Angeles during protests against immigration enforcement in June 2025 lacked legal justification. In his ruling, Breyer cited the 1878 Posse Comitatus Act, which prohibits the use of the U.S. military for civilian policing unless there is a rebellion or an emergency beyond the control of local authorities.

“Yet there was no rebellion, nor was civilian law enforcement unable to respond,” Breyer wrote, noting that 300 Guard members had been stationed in Los Angeles, setting up perimeters, using military vehicles, and engaging in crowd control. He added that plans were in place to expand the deployment to Oakland, San Francisco, and potentially other states.

The decision follows a three-day trial in August, where California officials argued that the troops performed policing functions, including detaining individuals, in support of Immigration and Customs Enforcement (ICE). State lawyers warned that allowing such deployments would mark “a vast and unprecedented shift in the role of the military in our society.”

Previously, the 9th U.S. Circuit Court of Appeals had allowed Trump to maintain temporary control over the Guard while California Governor Gavin Newsom challenged the deployment. The case is drawing national attention as Trump has also threatened to deploy troops to Chicago and other cities.

While Trump’s lawyers insisted the Guard only protected federal agents, Judge Breyer ruled the action unlawful, reinforcing limits on presidential authority to use the military on U.S. soil.