The United States Supreme Court ruled on Tuesday that a pandemic-era health measure used to limit immigration will say in place indefinitely.

The restriction, known as Title 42, has been used by officials to expel asylum seekers. In all, it has been deployed some 2.5 million times and turned away many more at the border.

Immigration advocates and the Biden administration moved to repeal the law, but 19 Republican-leaning states along the border pushed back with their own lawsuit to keep it in place.

"The court is not going to decide until June, apparently, and in meantime we have to enforce it. But I think it's overdue," Biden told reporters at the White House.

What did the Supreme Court say?

"The states contend that they face an immigration crisis at the border and policymakers have failed to agree on adequate measures to address it," the Supreme Court said in its 5-4 ruling on Tuesday.

"The only means left to mitigate the crisis, the states suggest, is an order from this Court directing the federal government to continue its COVID-era Title 42 policies as long as possible."

However, in their dissenting opinion, justices Neil Gorsuch and Ketanji Brown Jackson argued that "the current border crisis is not a COVID crisis."

What is Title 42?

Title 42 is named after the section of the 1944 public health law it is based on. But the rule was introduced under former US President Donald Trump in early 2020.

The measure allows authorities to remove foreigners without any legal process or formal deportation to their country of origin if they are found to have entered the country without a visa.

Critics branded Title 42 as an "inhumane" rule that was unfit as both health policy and immigration policy. Meanwhile, the Centers for Disease Control (CDC) said in April that vaccination rates meant the COVID-era policy was no longer necessary.

"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,'' said Lee Gelernt, a lawyer with the American Civil Liberties Union, which had been lobbying to end Title 42's use.

Ahead of Tuesday's ruling, thousands of migrants gathered on the Mexican side of the border.

The White House said it it is preparing to manage the border "in a secure, orderly, and humane way when Title 42 eventually lifts."