The Supreme Court on Tuesday ruled against the Biden administration in its attempt to end a controversial Trump-era border policy in a major blow to the president’s efforts to undo the hardline policies of his predecessor.

The court denied, 6-3, the Biden administration’s application to block an Aug. 13 order by a Texas federal judge to reinstate the policy, formally known as Migrant Protection Protocols, or MPP, which required asylum seekers to wait in Mexico while their claims were adjudicated in the United States.

The one-page ruling said the Biden administration had failed to show that rescinding MPP was not “arbitrary and capricious.” Justices Sonia Sotomayor, Elena Kagan and Stephen G. Breyer noted their dissent.

Texas and Missouri, which had filed suit to preserve the policy, said in briefs filed to the high court late Tuesday that the government’s argument — that the lower court ruling dictates U.S. foreign policy — “proves too much.”

Those states wrote that “implementing virtually any significant immigration policy may have collateral consequences for foreign relations. But the Government may not use such foreign-policy implications as a blank check to avoid complying with” immigration laws.

Soon after his inauguration, President Joe Biden moved to undo many of former President Donald Trump’s immigration policies through executive orders, including MPP. The Trump administration argued MPP discouraged asylum seekers, but immigration advocates said the policy denied people a legal right to seek protection in the U.S. and forced them to wait in dangerous Mexican border cities.

In June, the Department of Homeland Security formally ended the policy.

If allowed to stand, the court ruling maintaining the policy “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 Justice Department said in its request for a stay Friday to the Supreme Court.

It also argued the Aug. 13 order issued by U.S. District Judge Matthew J. Kacsmaryk of the Northern District of Texas, a 2019 Trump appointee, “imposes a severe and unwarranted burden on Executive authority over immigration policy and foreign affairs.” 

Immigrant advocacy groups, who have pushed for the policy’s end, said they would continue their efforts.

The National Immigration Law Center expressed disappointment with the Supreme Court action.

“We are committed to doing everything we can to prevent this egregious policy from harming one more person and will use every tool at our disposal to oppose the Remain in Mexico policy, or any like it, and we urge the Biden administration to do the same,” said Marielena Hincapié, the group’s executive director, in a statement.

Todd Ruger contributed to this report.