A federal judge on Friday paused the Trump administration’s efforts to fast-track the deportation of migrants who legally entered the United States through humanitarian parole programs, marking a win for immigrant rights groups who argued the policy was illegal and dangerous.

The decision could present a major hurdle for the Trump administration and bar federal immigration officers from summarily deporting hundreds of thousands of people.

In a world of bad options, they played by the rules,” wrote U.S. District Judge Jia Cobb of immigrants with parole status.