Civil rights attorneys sued the Trump administration Saturday to prevent it from transferring 10 migrants detained in the U.S. to Guantanamo Bay, Cuba, their second legal challenge in less than a month over plans for holding up to 30,000 immigrants there for deportation.

The latest federal lawsuit so far applies only to 10 men facing transfer to the naval base in Cuba, and their attorneys said the administration will not notify them of who will be transferred or when. Like a lawsuit the same attorneys filed earlier this month for access to migrants already detained there, the latest case was filed in Washington and is backed by the American Civil Liberties Union.

At least 50 migrants have been transferred already to Guantanamo Bay, and the civil rights attorneys believe the number now may be about 200. They have said it is the first time in U.S. history that the government has detained non-citizens on civil immigration charges there. For decades, the naval base was primarily used to detain foreigners associated with the Sept. 11, 2001, attacks.

Trump has said Guantanamo Bay, also known as “Gitmo,” has space for up to 30,000 immigrants living in the U.S. and that he plans to send “the worst” or high-risk “criminal aliens” there. The administration has not released specific information on who is being transferred, so it is not clear what crimes they are accused of committing in the U.S. and whether they have been convicted in court, or merely charged or arrested.

“The purpose of this second Guantanamo lawsuit is to prevent more people from being illegally sent to this notorious prison, where the conditions have now been revealed to be inhumane,” said Lee Gelernt, an ACLU attorney and lead counsel on the case. “The lawsuit is not claiming they cannot be detained in U.S. facilities, but only that they cannot be sent to Guantanamo.”

The 10 men are from nations including Afghanistan, Bangladesh, Pakistan and Venezuela, and their attorneys say they are neither high-risk criminals nor gang members. In a Jan. 29 executive order expanding operations at Guantanamo Bay, Trump said that one of his goals is to “dismantle criminal cartels.”

Their attorneys described their latest lawsuit as an emergency filing to halt imminent transfers and challenge the Trump administration’s plans. They contend that the transfers violate the men’s right to due legal process, guaranteed by the Fifth Amendment to the U.S. Constitution

The latest lawsuit also argues that federal immigration law bars the transfer of non-Cuban migrants from the U.S. to Guantanamo Bay and that the U.S. government has no authority to hold people outside its territory, and the naval base remains part of Cuba legally. The transfers are also described as arbitrary.

The men’s attorneys allege that many of the people who have been sent to Guantanamo Bay do not have serious criminal records or even any criminal history. Their first lawsuit, filed Feb. 12, said migrants sent to the naval base had “effectively disappeared into a black box” and couldn’t contact attorneys or family. The U.S. Department of Homeland Security, one of the agencies sued, said they could reach attorneys by phone.

In another, separate federal lawsuit filed in New Mexico, a federal judge on Feb. 9 blocked the transfer of three immigrants from Venezuela being held in that state to Guantanamo Bay. Their attorneys said they had been falsely accused of being gang members.

The migrant detention center at Guantanamo operates separately from the U.S. military’s detention center and courtrooms for foreigners detained under President George W. Bush during what Bush called its war on terror. It once held nearly 800 people, but the number has dwindled to 15, including 9/11 mastermind Khalid Sheikh Mohammed.

Defense Secretary Pete Hegseth, who was assigned to Guantanamo when he was on active duty, has called it a “perfect place” to house migrants, and Trump has described the naval base as “a tough place to get out of.”

A United Nations investigator who visited the military detention center in 2023 said conditions had improved, but military detainees still faced near constant surveillance, forced removal from their cells and unjust use of restraints, resulting in “ongoing cruel, inhuman and degrading treatment under international law.” The U.S. said it disagreed “in significant respects” with her report.