A federal judge on Monday blocked a recently-enacted Trump administration policy of returning U.S. asylum seekers to Mexico while they wait for their cases to be heard in immigration court – a move President Trump called “unfair” on twitter.

The decision to halt the policy was handed down in San Francisco by U.S. District Judge Richard Seeborg, who said in his ruling that the policy doesn’t ensure the protection of migrants waiting in Mexico “from undue risk to their lives or freedom.”

The Trump administration rolled out the policy in January in San Diego, the nation’s busiest border crossing.

Before then, it was common for asylum-seekers to be released in the U.S. with notices to appear in court.

President Donald Trump on Monday night tweeted his dissatisfaction with the ruling, writing, “ A 9th Circuit Judge just ruled that Mexico is too dangerous for migrants. So unfair to the U.S. OUT OF CONTROL!”

Monday’s ruling was the result of a legal request to halt the practice on behalf of 11 Central American asylum seekers and legal advocacy groups.

Seeborg said he won’t enforce his decision until Friday in order to give the government a chance to ask an appeals court to put the ruling on hold.

As of Monday night, it wasn’t clear if the Trump administration would take that step.