The Department of Homeland Security on Thursday told hundreds of thousands of migrants that their permission to live and work in the United States had been revoked and they should leave the country, according to a copy of the notice obtained by CNN.

The termination notice was addressed to nationals of Cuba, Haiti, Nicaragua and Venezuela who came to the United States through a Biden-era parole program. More than half a million people from those four countries benefited from the program, though it’s unclear how many have since sought other forms of immigration relief while in the United States. The notice, according to DHS, was sent to email addresses provided by those in the program.

“This notice informs you that your parole is now terminated,” the notice reads. “If you do not leave, you may be subject to enforcement actions, including but not limited to detention and removal, without an opportunity to make personal arrangements and return to your country in an orderly manner.”

The notice also states that work permits linked to the program will be revoked and directs parolees to return those permits to US Citizenship and Immigration Services.

Thursday’s move is the latest step in the Trump administration’s aggressive and wide-ranging effort to encourage or force millions of migrants out of the country, whether they are in the U.S. legally or illegally.

The Biden administration announced in 2023 that it would grant parole to qualified migrants from Cuba, Haiti, Nicaragua and Venezuela who submitted to review by authorities rather than attempting to enter the country illegally. Applicants were required to have an American sponsor or US-based sponsor who’s lawfully present in the country and clear security vetting.

The program became a political flashpoint as Republicans argued the administration was misusing parole authority and overreached in establishing the program for those countries. At the time, Biden officials credited the program for driving down border crossings by instead providing a path for migrants to apply to legally migrate to the US.

President Donald Trump signed an order on his first day in office seeking to unilaterally end the program. That move prompted legal challenges that eventually made their way to the Supreme Court, which allowed Trump to strip protections for beneficiaries of the parole program.

“Ending the CHNV parole programs, as well as the paroles of those who exploited it, will be a necessary return to common-sense policies, a return to public safety, and a return to America First,” Homeland Security Assistant Secretary Tricia McLaughlin told CNN in a statement.

Though the emergency decision from the Supreme Court is not final – the underlying legal case will continue in lower courts – the order allowed the administration to expedite deportations for an estimated 530,000 migrants who had previously benefited from the program.

The Trump administration told the Supreme Court that its decision to terminate parole status for the migrants at issue was one of the “most consequential immigration policy decisions” it has made. Lower court orders temporarily blocking its policy, the administration said, upended “critical immigration policies that are carefully calibrated to deter illegal entry, vitiating core executive branch prerogatives, and undoing democratically approved policies that featured heavily in the November election.”

This article has been updated with additional developments.

CNN’s Devan Cole and John Fritze contributed to this report.