The Supreme Court has ruled that migrants arriving at the US-Mexico border are not entitled to apply for asylum until they set foot in the country.

The 6-3 ruling will allow President Donald Trump, a Republican, to revive a policy first used in 2016, but rescinded in 2021 under the Democratic administration of President Joe Biden.

Under federal law, a migrant who "arrives" in the US may apply for asylum, which the Trump administration had argued ruled out those stopped on the Mexican side of the border.

In a separate ruling, the top court ruled that the Trump administration can strip more than 356,000 Syrian and Haitian immigrants of temporary protections that allows them to stay in the US.

Justice Alito delivered the opinion of the court on Thursday, calling the case "straightforward".

"In ordinary speech, no one would say that a person 'arrives in' a place . . . before the person enters that place," he said in his opinion.

The decision in Noem v Al Otro Lado means the Trump administration has won its appeal against a lower court ruling that found the asylum turn-back policy was unlawful.

The policy is called "metering" because US immigration authorities can use it to limit the number of asylum seekers allowed to request protection each day on the grounds that they are too overburdened to process additional claims.

Under federal law, any non-citizen who is "physically present in the United States" or "arrives in the United States" can file an official claim that they are fleeing political, racial or religious persecution in their home country.

A lawyer for an immigrant advocacy group had argued that asylum seekers arrive in the US when they reach a port of entry.

When this case reached the Supreme Court in March, arguments focused on what it means to arrive in the US.

Justice Amy Coney Barrett, a conservative, asked: "What is the magic thing, or the dispositive thing, that we're looking for where we say, 'Ah, now that person, we can say, arrives in the United States?'"

Justice Neil Gorsuch, another conservative, asked whether a migrant at the back of the queue at a port of entry, or at the water's edge of the Rio Grande, which flows along the border with Mexico, had arrived in the US.

Vivek Suri, an assistant to the solicitor general, arguing for the Trump administration, told the court: "You can't arrive in the United States while you're still standing in Mexico. That should be the end of this case."

But Kelsi Corkran, of the Institute for Constitutional Advocacy and Protection, who represented the migrants, told the court that migrants have arrived in the US when they are at the "threshold of the port's entrance about to step over".

After he returned to office in 2025, Trump also announced a more sweeping ban on asylum at the border, which is separate from the metering policy and faces an ongoing legal challenge, too.