SAN FRANCISCO (AP) — A U.S. judge in San Francisco has blocked the Trump administration’s policy of returning asylum seekers to Mexico as they wait for a court to hear their cases, but the order won’t immediately go into effect.

Judge Richard Seeborg on Monday granted a request by civil liberties groups to halt the practice while their lawsuit moves forward. The decision is on hold until Friday to give U.S. officials the chance to appeal.

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Children part of the Central American migrants caravan, play on the street, while camping near a closed temporary shelter a few meters from the US-Mexico border in Tijuana, Baja California State, Mexico, December 4, 2018. (credit: Guillermo Arias/AFP/Getty Images)

The groups say the policy violates U.S. law by failing to adequately evaluate the dangers that migrants face in Mexico.

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President Donald Trump’s administration says the policy responds to a crisis at the southern border that has overwhelmed the ability of immigration officials to detain migrants.

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The launch of the practice in January marked an unprecedented change to the U.S. asylum system.