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.