US President Donald Trump has signed an executive order to temporarily suspend the approval of some green cards.
The order, which contains a number of exemptions, is to last for 60 days and then could be extended, he said.
Mr Trump said the policy was designed to protect American workers’ jobs in an economy pummelled by the coronavirus.
Critics have accused him of using the pandemic as cover to ram through long-sought hardline immigration policies ahead of November’s election.
“This will ensure that unemployed Americans of all backgrounds will be first in line for jobs as our economy reopens,” Mr Trump said at Wednesday’s coronavirus briefing at the White House.
The hundreds of thousands of temporary work visas issued by the US each year will not be affected by the 60-day pause.
Also exempt are the spouses and young children of American citizens, green card applicants currently already in the US, and those seeking entry to work as doctors, nurses or other healthcare professionals.
But the measure is expected to curtail the practice of green card holders sponsoring their extended families, which the president calls chain migration.
The president’s order is expected to face legal challenges.
How did we get here?
The president vowed to suspend “all immigration” to the US on in a tweet on Monday night.
The announcement was met with a swift backlash, including from some business leaders, due to fears it could limit temporary working visas for people like farm labourers and hi-tech employees.
The final order has been heavily watered down, meaning the 60-day hold applies only to permanent residents, not temporary workers.
Why is Trump doing this?
The president says he is seeking to protect American jobs.
More than 20 million Americans have lost their jobs amid the coronavirus outbreak, and the president has said the government had a “solemn duty” to ensure they regain work.
“It would be wrong and unjust for Americans laid off by the virus to be replaced with new immigrant labour flown in from abroad,” he said on Tuesday.
Mr Trump, a Republican, came into office partly because of his hardline stance on immigration and has made the issue central to his presidency.
Some suspect the president is playing to his support base with one eye on November’s election, when he is expected to face off against former Vice-President Joe Biden, a Democrat.
Others have accused the president of trying to distract attention from his response to the coronavirus.
The US has seen more than 46,000 deaths and 840,000 infections, the most in the world.