The memo leaves unclear exactly who could be deported.
Frantzdy Jerome, a Haitian migrant who had scheduled an appointment at a port of entry along the southern border, was admitted into the country in June. Within weeks, he was issued a work permit, and he has been working the overnight shift at an Amazon warehouse in the Midwest. He worries that he could be designated for deportation.
“The news is overwhelming me with fear,” said Mr. Jerome, 33, who has a young child in the United States and supports 12 people in his home country.
“So many Haitians work at Amazon, and we are all nervous about the situation,” he said.
At a New York migrant shelter, Elhadi Youssouf Diagana, 34, of Mauritania, said that some people had not left the facility.
“There’s people who work, who work for Uber, who deliver food, they don’t want to go outside,” Mr. Diagana added. “They’re there, they don’t move.”
Wilfredo O. Allen, an immigration lawyer in Miami, said that when he went to have breakfast at a Cuban restaurant on Friday, several workers — some of whom are already his clients — peppered him with questions about whether they could be deported.
“Today, in Miami, there is fear,” he said.
Experts said that immigrants had every reason to worry because the memo turned hundreds of thousands of people who have been in the country lawfully into unauthorized immigrants.
“After they came in doing everything the government told them to do, they are in the same boat as someone who came here unlawfully,” said Lynden Melmed, former chief counsel at U.S. Citizenship and Immigration Services.
“Right now, even though you are holding valid documents that allow you to work and be in the U.S., this guidance makes you vulnerable to being picked up by immigration agents and arrested at any time,” said Mr. Melmed, a partner at the firm Berry Appleman & Leiden.
Former President Biden used executive authority to admit people with temporary statuses that do not automatically offer a path to permanent residence. But, crucially, the initiatives shielded beneficiaries from deportation for at least two years and allowed them to work legally
The memo issued late on Thursday by Benjamine C. Huffman, the acting homeland security secretary, directs immigration agents to identify for expedited removal the population of migrants who benefited from two specific Biden-era initiatives related to border management.
One was a U.S. Customs and Border Protection app called CBP One that migrants used to schedule appointments to enter the United States (and to discourage unscheduled, unauthorized entries). The other was a program that allowed more than 500, 000 people from four troubled countries — Cuba, Nicaragua, Venezuela and Haiti — to fly directly to the United States if they had a financial sponsor in the United States. Both initiatives were popular, and the Biden administration credited them with helping reduce a surge in unauthorized crossings over the southern border.
The migrants were given a grant to stay in the country for up to two years under a temporary legal status known as “parole.”
Separately, the Trump administration ordered an immediate pause of another Biden parole program that has allowed more than 150,000 Ukrainians to enter the United States if they had financial backers, according to an email obtained by the Times.
Advocates of immigrants said they feared that an initiative that has brought Afghans since the U.S. military withdrawal, could also be at risk.
President Trump’s executive orders and the memo have ushered in a new era of immigration enforcement that appears to be far more sweeping than anything seen in decades.
Previous administrations, even Republican ones, prioritized the arrest and removal of people with criminal records, given the limited resources for enforcement. But while some Trump officials have said they, too, will prioritize people with criminal records, the administration’s early actions have made clear they aim to cast a far wider net.
The memo suggests that agents review the cases of immigrants who have not applied for asylum within one year of entering the United States.
Many people who entered the country when Mr. Biden was still president have Temporary Protected Status, or T.P.S., a designation given to people from countries that the executive branch deemed to be in extreme turmoil because of a humanitarian crisis, political upheaval or a natural disaster. That allows nationals from those countries already in the United States to stay.
Before leaving office, the Biden administration extended T.P.S. for immigrants from many countries for at least until 2027, and they are likely to remain shielded from removal, even after the recent memo. Others have asylum applications, which should protect them.
Experts said that the most vulnerable to immediate enforcement were likely those who crossed the border recently using the CBP One app. Often, they had waited months in Mexico for the moment their phone screens flashed with a notice instructing them to report to a port of entry along the southern border at a specific date and time.
They were then paroled into the country. Within weeks, they typically had employment authorization and Social Security numbers and were able to start working.
Guillermo Estrada, 40, who was at a shelter in Brownsville, Texas early this week, had used the app. He said he and others at the shelter felt that they “were the lucky ones” for making it into the United States before Mr. Trump returned to office.
“We did it the right way. We did not cross illegally,” Mr. Estrada said. “We could have crossed through the river. But we waited.”
He and others were left to wonder what Mr. Trump’s aggressive moves would mean going forward.
After news on Friday of the memo, one word kept coming up: fear.
“Of course we are afraid. We are all feeling the same fear,” Mr. Estrada said on Friday.
“If we get deported to Mexico, the mafia is there,” he said. “If we get deported to Venezuela, the government is waiting for us.”
Mr. Estrada said he was persecuted in Venezuela for expressing his views against the current government. He pointed to a bullet wound on an ankle that he said was inflicted by a Venezuelan soldier.
“Imagine, where are we going to go? I spent thousands of dollars to get here,” he said. “If everything was fine in Venezuela, I would have returned on my own.”
The man who runs the shelter in Brownsville, Victor Maldonado, could not offer the migrants reassurance. He said he had seen ICE trucks circling the shelter in the last few days. “It looks like they were scouting,” Mr. Maldonado said. “We just don’t know if they can come in and pick up people who don’t have work permits. There are a lot of unknowns.”
Representative María Elvira Salazar, a Miami Republican, sent a letter to Homeland Security urging the department to protect from deportation Cubans, Venezuelans, Nicaraguans and Haitians who do not have criminal records or pending deportation cases.
But the memo directs agents to “take all steps necessary” to review immigrants’ cases and exercise discretion to determine whether they can be subjected to expedited removal, which deprives people from going before a judge to fight to remain in the country.
Some countries might not accept repatriated nationals. Regardless, many migrants said that they could not countenance a return.
Mr. Jerome said that family members in Haiti had been murdered by gangs who have taken control of large swaths of the country.
For now, “I will keep working with a lot of fear,” he said a few hours before heading to his shift at the Amazon warehouse. He also wondered whether Jeff Bezos, the founder of the company, might somehow be able to help.
“Maybe Bezos can do something for the people working for him because he’s friends with Trump,” he said.
Patricia Mazzei contributed reporting from Miami and Olivia Bensimon contributed reporting from New York.