"We encourage you to register as soon as possible," officials said on the U.S. Citizenship and Immigration Services website.
Federal officials have said they will end temporary protection for Salvadorans, Nicaraguans and Haitians, and they gave each group a grace period to prepare to return home as long as they re-register with the government.
Congress created the temporary protection program in 1990 to shield immigrants from deportation to homelands consumed by war, natural disasters or other extraordinary events.
The Trump administration has said that past presidents abused the program by allowing it to last long after the initial crises had subsided.
The federal government approved protected status for Salvadorans 17 years ago, following two devastating earthquakes in the Central American nation. On Jan. 8, Homeland Security Secretary Kirstjen Nielsen said conditions in El Salvador had improved since the quakes and the protection was no longer justified for that reason. Their protection expires in September 2019.
In November, the Department of Homeland Security said TPS for Haitians will end in July 2019; they received protection from deportation after a 2010 earthquake.
About 2,500 Nicaraguans granted protection after Hurricane Mitch in 1998 will see their protection terminate in January 2019. Officials earlier had said that Nicaraguans must apply to renew their work permits by Feb. 13.
Salvadoran TPS recipients are the largest group by far, and they include those who came to the United States illegally or arrived with permission but overstayed their visas. Many came before the earthquakes. Once in the program, they were able to obtain steady jobs, driver's licenses and social security cards.
TPS holders from El Salvador have sent millions of dollars home to aid family members and are parents to an estimated 190,000 children who were born in this country and are U.S. citizens, studies show. The largest number of recipients, some 32,000 people, reside in the Washington area, followed by Los Angeles, New York and Houston.
Advocates say El Salvador is unable to absorb a massive influx of its citizens and had urged U.S. officials to extend the protected status instead of moving to phase it out. The nation has one of the world's highest homicide rates, fueled by gang violence, and it is one of the poorest countries in the hemisphere.
Salvadorans with TPS are among nearly 1 million immigrants facing the loss of their work permits under President Trump.
The largest group is 690,000 undocumented immigrants brought to the United States when they were children and shielded from deportation under an Obama-era program called Deferred Action for Childhood Arrivals (DACA), which will be phased out starting in March unless Congress and the White House agree to pass a law granting recipients permanent legal status.