In a first-in-the-nation ruling on a hotly contested Trump administration policy, a federal judge ordered a halt Wednesday to arrests of migrants at immigration courthouses in Northern California, saying the detentions are unjustified and have discouraged people from attending critical hearings.

“Widespread” arrests at the courthouse are having a “chilling effect on noncitizens’ participation in removal proceedings” and their ability to contest deportation, U.S. District Judge P. Casey Pitts of San Francisco wrote in an order blocking further arrests.