The ruling blocks a new tactic employed by the Trump administration: detaining immigrants outside court appearances and putting them into a sped-up deportation process known as expedited removal.

A federal judge has agreed to temporarily block the Trump administration’s efforts to expand fast-track deportations of immigrants who legally entered the U.S. under a process known as humanitarian parole.

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