WASHINGTON (AP) — Migrants from Brazil who seek U.S. asylum at the southern border will now have to wait in Mexico to learn their fate along with tens of thousands of others turned back under a year-old Trump administration policy.

The Department of Homeland Security said Wednesday that it has begun sending Brazilians back into Mexico amid a surge of people from the South American country seeking refuge in the United States.

DHS said in a statement announcing the change that the number of Brazilian migrants arriving at the southern border had tripled over the past year. They will join about 55,000 migrants waiting in Mexico for rulings on their asylum claims, decisions that can take months or even years.

Previously, migrants presenting themselves at the southern border or apprehended while trying to enter the country were, if they met the initial threshold for asylum, often released on parole in the U.S. to await a final determination by an immigration judge.

President Donald Trump’s administration began forcing them to stay in Mexico as part of a broader effort to reduce what DHS calls “irregular migration” to the United States.

Advocates for immigrants have sued the federal government to halt the policy, known informally as “remain in Mexico,” arguing it deprives people of the right under international law to seek asylum and makes it harder for them to press their legal cases in backlogged immigration courts.

The U.S. began returning migrants from Central America to Mexico last year. In December, acting Customs and Border Patrol Chief Mark Morgan vowed to try to shut down asylum for migrants from outside the immediate region, noting migrants from Haiti, Brazil and African countries.