An order signed by Chief Justice John Roberts placed an emergency stay on the removal planned for Wednesday of Title 42, which allowed the government to use Covid-19 safety protocols to summarily block the entry of millions of migrants.
Roberts placed government immigration policy on temporary hold in response to a last-minute petition from 20 states arguing that ending Title 42 would create a gush in migrants that would overwhelm their services.
They cited the Department of Homeland Security predicting that border crossings, mostly by Mexicans and other Latin Americans asking for asylum, could triple to 18,000 every day.
"The greatly increased number of migrants resulting from this termination will necessarily increase the States' law enforcement, education, and healthcare costs," the states argued.
The move came after an appeals court in Washington ruled last Friday that there was no longer justification for using Title 42 to sweepingly reject asylum-seekers.
The policy was put in place in March 2020, in Trump's final year in office, as the coronavirus pandemic swept into the United States.
The administration of President Joe Biden had previously accepted a lower court ruling that Title 42 was no longer justified to block asylum seekers and other migrants.
Last week the White House said the Department of Homeland Security was prepared to deal with the expected surge, but gave few details on how it would do that.
"We have an intensive all-of-government effort underway to prepare," said White House Spokeswoman Karine Jean-Pierre.
DHS said in a statement that Title 42 will remain in effect as a result of the high court's stay order, and that "individuals who attempt to enter the United States unlawfully will continue to be expelled to Mexico."
While litigation proceeds, "we will continue our preparations to manage the border in a safe, orderly, and humane way when the Title 42 public health order lifts," the department said.
Conservative lawmakers swiftly commended the stay, with some urging that Title 42 be codified in US law.
Top House Republican Kevin McCarthy said he was "glad to see the Supreme Court inject some temporary sanity into the situation."