A divided Supreme Court on Tuesday sided with a group of mostly Republican-led states and ordered the pandemic-era public health protocol known as Title 42 -- which started in the early days of COVID-19 and allows the expulsion of migrants at the border -- to remain in place pending a hearing before the justices.
The 5-4 decision reverses lower court decisions that Title 42 had to end in December and means that the policy will remain in effect until a final ruling.
The Supreme Court scheduled oral arguments on the appeal for February but said in a statement that "the stay itself does not prevent the federal government from taking any action with respect to that policy."
In other words, in the court's view, the Biden administration still has the power and prerogative to discontinue the policy on its own if it so chooses.
The court said it was preparing to examine a narrow, procedural question unrelated to the merits of Title 42 itself: whether the states challenging the policy may intervene to challenge the district court's summary judgment order.
Justices Samuel Alito, Brett Kavanaugh, Amy Coney Barrett, John Roberts and Clarence Thomas, all members of the conservative wing, agreed to grant a hearing on the appeal.
Justices Sonia Sotomayor and Elena Kagan indicated that they would have denied the application from the states. Justice Neil Gorsuch -- the lone Republican appointee not to vote to grant the request -- and Justice Ketanji Brown Jackson also would have denied the application, writing in dissent that "we are a court of law, not policymakers of last resort."
U.S. District Judge Emmet Sullivan previously set a Dec. 21 deadline to terminate the fast-track expulsion order, finding it "arbitrary and capricious," with minimal public health impact despite its purported purpose to slow the spread of COVID-19.
That date will now be pushed back for several months until the Supreme Court holds its hearing and issues its ruling.
Nineteen states intervened after Sullivan's decision in November. They have contended that Title 42 ending would create a "crisis" of unauthorized migration that would unduly burden law enforcement, education and health care services.
Their appeal was denied in December and the states filed an emergency application with Supreme Court Chief Justice Roberts on Dec. 19.
Roberts, who oversees the appellate circuit handling the case, initially granted a temporary stay later that day, allowing the court time to consider the application.
The justices have now agreed to hear the states' appeal and issued a longer stay until after their decision on Title 42's fate.
Migrant and civil rights advocates argue Title 42 illegally prevents people from making asylum claims while trying to enter the U.S.
White House press secretary Karine Jean-Pierre said in a written statement that the Biden administration would "of course, comply with the order and prepare for the Court's review."
"The Supreme Court's order today keeps the current Title 42 policy in place while the Court reviews the matter in 2023," she said. "We will, of course, comply with the order and prepare for the Court's review."
Jean-Pierre called on Congress to pass comprehensive immigration reform.
"Today's order gives Republicans in Congress plenty of time to move past political finger-pointing and join their Democratic colleagues in solving the challenge at our border by passing the comprehensive reform measures and delivering the additional funds for border security that President Biden has requested," she said.
The Department of Homeland Security said in a statement, in part: "As required by today's Supreme Court order, the Title 42 public health order will remain in effect and individuals who attempt to enter the United States unlawfully will continue to be expelled to Mexico or their home country. People should not listen to the lies of smugglers who take advantage of vulnerable migrants, putting lives at risk. The border is not open, and we will continue to fully enforce our immigration laws."
In a statement, Lee Gelernt, the lead lawyer for the ACLU's challenge to Title 42, said: "We are deeply disappointed for all the desperate asylum-seekers who will continue to suffer because of Title 42, but we will continue fighting to eventually end the policy."
"Notwithstanding the Supreme Court's ruling, nothing prevents the administration from revoking the Title 42 policy after notice and comment to the public," Gelernt told ABC News.
"At the end of the day, this is not about whether temporarily Title 42 stays in effect or not," ABC News contributor and former head of DHS intelligence John Cohen said. "It is about how -- as a nation -- we are going to address the crisis posed by the millions of displaced persons in Central and South America, who fled violence, persecution, COVID and economic crisis and who seek the protection and economic opportunities that come by their entering the U.S."
"It is a crisis that will not be solved by political posturing, bus trips and calls to close the border," Cohen added. "It will be solved through a cohesive and comprehensive plan that involves bringing together federal, state, local and private sector resources."
ABC News' Armando Garcia, Benjamin Gittleson and Luke Barr contributed to this report.