A United States Air Force Boeing C-17 used for deportation flights is pictured at Biggs Army Airfield in Fort Bliss, El Paso, Texas on February 13, 2025.

A United States Air Force Boeing C-17 used for deportation flights is pictured at Biggs Army Airfield in Fort Bliss, El Paso, Texas on February 13, 2025. / AFP via Getty Images

Immigration attorneys have asked a Massachusetts federal judge to block an alleged Trump administration move to deport migrants to a third country, in this case South Sudan.

They also urged federal Judge Brian Murphy to immediately order the return of any migrants who may have already been deported to these "third countries," or places they're not from originally, according to a court filing on Tuesday.

Migrants from Myanmar, Vietnam and other countries who do not have legal status to remain in the U.S. received notices on Monday that they would be deported, their lawyers said.

When lawyers representing detainees sought to contact them on Tuesday, officials at the Port Isabel Detention Center in Texas said that at least one person, originally from Myanmar, had already been removed to South Sudan, according to a declaration from their attorney.

"Plaintiffs ask this Court for an immediate order ordering the immediate return of any class members removed to South Sudan," according to documents filed in the U.S. District Court in Massachusetts. The attorneys also asked the government not to deport migrants to any country which isn't their country of origin unless they get proper written notice and enough time to contest their deportation.

They argued that the Trump administration's actions to deport their clients also violate the judicial order barring deportations to such third countries without adequate due process.

The Department of Homeland Security didn't immediately respond to a request for comment.

The Trump administration has been negotiating with other countries willing to take in people deported from the U.S.

The Department of Homeland Security has already deported more than 200 Venezuelan migrants to El Salvador. It argued that some of the men were members of the Tren de Aragua gang and could be deported using the Alien Enemies Act, an obscure wartime law that allows for quick removals. The Trump administration has also paid El Salvador $6 million to house them.

Earlier in May, the administration had sought to send migrants to Libya, despite concerns from human rights groups about the violence there and the country's notorious human rights record.

South Sudan endured a long civil war that killed more than 50,000 people until a fragile peace halted the fighting in 2018. Even so, political instability persists and clashes between rebels and the government continue. Many, including the United Nations, worry about the prospect of the country tipping into civil war again.