The Supreme Court on Tuesday refused to block a court ruling ordering the Biden administration to reinstate a Trump-era policy that forces people to wait in Mexico while seeking asylum in the U.S.

With the three liberal justices in dissent, the court said the administration likely violated federal law in its efforts to rescind the program informally known as Remain in Mexico.

It’s not clear how many people will be affected and how quickly. Under the lower court ruling, the administration must make a “good faith effort” to restart the program.

A federal judge in Texas had previously ordered that the program, formally called Migrant Protection Protocols, be reinstated last week. Both he and the 5th U.S. Circuit Court of Appeals refused the administration’s request to put the ruling on hold.

Justice Samuel Alito ordered a brief delay to allow the full court time to consider the administration’s appeal to keep the ruling on hold while the case continues to make its way through the courts.

The 5th Circuit ordered expedited consideration of the administration’s appeal.

The court offered little explanation for its action, although it cited its opinion from last year rejecting the Trump administration’s effort to end another immigration program, Deferred Action for Childhood Arrivals. In that case, the court held that the decision to end DACA was “arbitrary and capricious,” in violation of federal law.

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The administration has “failed to show a likelihood of success on the claim that the memorandum rescinding the Migrant Protection Protocols was not arbitrary and capricious,” the court wrote Tuesday in an unsigned order.

The three dissenting justices did not write an opinion expressing their views of the case.

During Donald Trump’s presidency, the policy required tens of thousands of migrants seeking asylum in the U.S. to turn back to Mexico. It was meant to discourage asylum seekers but critics said it denied people the legal right to seek protection in the U.S. and forced them to wait in dangerous Mexican border cities.

The judge, U.S. District Judge Judge Matthew J. Kacsmaryk, ordered that the program be reinstated in response to a lawsuit filed by the states of Texas and Missouri, whose governors have been seeking to reinstate some of the hard-line anti-immigration policies of the Trump administration.

The Biden administration argued in briefs that the president has “clear authority to determine immigration policy” and that Homeland Security Secretary Alejandro Mayorkas had discretion in deciding whether to return asylum seekers to Mexico.

In its brief to the Supreme Court on Friday, the administration argued that the policy had been dormant for more than a year and that abruptly reinstating it “would prejudice the United States’ relations with vital regional partners, severely disrupt its operations at the southern border, and threaten to create a diplomatic and humanitarian crisis.”

The Trump administration largely stopped using the “Remain in Mexico” policy at the start of the pandemic, at which point it began turning back virtually everyone crossing the Southwest border under a different protocol — a public health order that remains in effect. The Biden administration said the pre-pandemic policy had been “largely dormant” for months even before the outbreak of COVID-19.

President Joe Biden suspended the program on his first day of office and the Homeland Security Department ended it in June.

Kacsmaryk was nominated to the federal bench by Trump. The 5th Circuit panel that ruled Thursday night included two Trump appointees, Andrew Oldham and Cory Wilson, along with Jennifer Walker Elrod, nominated to the appeals court by President George W. Bush.