The Trump administration has decided to cancel permits that allow nearly 200,000 people from El Salvador to live and work in the US.
They were granted Temporary Protected Status (TPS) after earthquakes rocked the Central American country in 2001.
Salvadoreans now have until 2019 to leave or face deportation, unless they find a legal way to stay.
The Trump administration has already removed TPS protection from tens of thousands of Haitians and Nicaraguans.
Protections for Salvadoreans were set to expire on Monday, after nearly two decades of holding the humanitarian status due to the impact of the natural disaster that killed more than 1,000 people.
The latest announcement comes four months after the government said it planned to scrap an Obama-era scheme, Daca, that protected young undocumented immigrants, mostly Latin Americans, from deportation.
Lawmakers in Congress have been given until March to decide on the fate of the 800,000 so-called Dreamers affected by the Daca decision.
What does it mean for Salvadoreans in US?
Their protection will not be terminated until 9 September 2019 "to allow for an orderly transition", the Department of Homeland Security said in a statement announcing the decision on Monday.
"The original conditions caused by the 2001 earthquakes no longer exist," the agency said.
"Thus, under the applicable statute, the current TPS designation must be terminated."
Who will be most affected?
The move will end the protected status of nearly 200,000 Salvadoreans living across America, forcing them to face possible deportation or separation from their families.
It also raises questions about the future of about 270,000 of their children who were born in the US, and who are also at risk of deportation.
Salvadoreans with Temporary Protected Status are established in large numbers in Los Angeles, Houston and New York.
According to the Center for Migration Studies, they represent more than 135,000 households across the country, with a quarter of them home-owners:
88% part of the labour force
10% self-employed
10% married to US citizens
El Salvador country profile
What is Temporary Protected Status?
The programme was created in 1990 and authorises immigrants from several countries to live and work in the US lawfully, regardless of whether they entered the country legally or not.
It is only granted to countries affected by armed conflict, environmental disaster, or epidemics.
With nearly 200,000 immigrants in the US, El Salvador represents the largest group of TPS recipients.
Ten countries, making up over 300,000 US immigrants, have been granted TPS protections since it was first signed into law by President George Bush.
Salvadoreans received TPS in March 2001 after two earthquakes devastated communities in El Salvador.
Over the next 15 years, the programme was reauthorised by US presidents several times.
What has reaction been in El Salvador?
The Salvadorean government has been lobbying the US to extend protections for people from their country living in the US.
El Salvador Foreign Minister Hugo Martinez said last week that ending TPS "would mean breaking up families that are in the United States".
He noted that due to the US practice of granting citizenship to babies born inside the United States, there were now nearly 200,000 US citizens who were born to parents who now may face deportation.
Money earned and sent back to families back in El Salvador also makes a valuable contribution to the country's economy, the Center for American Progress says. The think tank estimates that in 2015, remittances made up more than 15% of El Salvador's GDP.