The Trump administration on Friday issued a sweeping policy directive requiring most temporary visa holders and humanitarian parolees living in the U.S. to return to their home countries to apply for and complete their green card applications.

The policy memo issued by U.S. Citizenship and Immigration Services as part of the Trump administration’s immigration crackdown, instructs agency officers to treat U.S.-based “adjustment of status” applications as an “extraordinary form of relief.”

“We’re returning to the original intent of the law to ensure aliens navigate our nation’s immigration system properly,” U.S. Citizenship and Immigration Services spokesperson Zach Kahler said in a statement. “From now on, an alien who is in the U.S. temporarily and wants a Green Card must return to their home country to apply, except in extraordinary circumstances.”

Immigration lawyers told ABC News the new policy could impact hundreds of thousands of people with temporary work visas who are pursuing permanent residency from within the United States. 

Rosanna Berardi, an immigration lawyer in New York, said the policy would affect any foreign national with a pending U.S.-filed green card application, including legal workers and humanitarian parolees. 

“Afghans who assisted U.S. forces, Ukrainians fleeing war, face a specific trap: The memo treats their choice to apply for a green card inside the U.S. as an adverse factor, because their admission was temporary,” Berardi said. “Many have nowhere safe to return to.”

Immigration attorney Todd Pomerleaus said the Immigration and Nationality Act allows individuals who were legally inspected and admitted into the country to adjust their status from within the U.S.

“You can’t, through a stroke of a pen, overturn a statute,” he said. “I think it’s illegal, and it’s going to get shut down in court very quickly,” Pomerleau said. 

Shev Dalal-Dheini, the senior government director of the American Immigration Lawyers Association, told ABC News that Congress designed the U.S.-based adjustment framework to prevent families from being separated and to ensure U.S. companies could retain employees during visa backlogs.

“Since the 1950s, Congress has specifically allowed non-immigrants to adjust their status in the United States to that of a green card, and over the course of years they’ve slowly expanded that eligible class,” Dalal-Dheini said. “The statutory scheme is pretty well set, and it’s been around for many, many decades.” 

“This administration says they’re going to go after people who are criminals, but in the same breath, they are upending [the process] for people who are trying to follow the law,” Dalal Dheini said. “These are individuals who came here legally or were admitted legally … and now overnight, without any advance warning, through a policy memo, they are upending it.”