Also exempt from the order are members of the military and their children, as well as Iraqis and those from Afghanistan who obtain a visa by assisting military operations. The policy could, however, be expanded; Mr. Trump’s top cabinet officials will convene in at least 30 days to review any restrictions on “nonimmigrant visas,” including visas for seasonal workers.

While the president often rails against illegal immigration and promotes the construction of a wall along the southwestern border, the order is focused on the family-based immigration he and his allies have frequently assailed as “chain-based migration.”

“It would be wrong and unjust for Americans laid off by the virus to be replaced with new immigrant labor flown in from abroad,” Mr. Trump said on Tuesday. “We must first take care of the American worker.”

But as the pandemic touches every corner of daily life, including the economy, few employers are reaching out for workers at home or abroad. And critics have emphasized research that shows immigrants have a positive effect on the economy. Immigrants and their potential employers are also already subject to a certification process to ensure that there are an insufficient number of American workers to fill any potential job.

“He’s saying the system, the labor protections existing in the statute right now, are not good enough,” said Theresa Cardinal Brown, the director of immigration and cross border policy at the Bipartisan Policy Center. The executive order “means families will be separated, employers who have spent a lot of money and a lot of time to say, ‘This is the person I need for my company,’ will not have that person, and I can imagine they will not take kindly to this,” Ms. Brown said.