Guatemalans who were deported from the United States arrive to La Aurora International airport in Guatemala City in August 2019. During his campaign, President-elect Donald Trump promised to increase deportations starting on “day one” of his administration, though he has provided few details about how he would execute that plan. Moises Castillo/Associated Press file

Civil-liberties lawyers alarmed by President-elect Donald Trump’s plan to launch mass deportations of undocumented immigrants sued the federal government Monday for information about how authorities might quickly remove people from the United States.

The federal lawsuit alleges that U.S. Immigration and Customs Enforcement has failed to respond to requests for basic information about its existing contracts with private airline companies that make up “ICE Air,” as well as ground transportation services, airfields and policies governing deportation flights, including those carrying children.

Lawyers said the information is urgent because of Trump’s election victory this month and his upcoming inauguration on Jan. 20. Advocates for immigrants have accused ICE and its contractors of treating migrants harshly and holding them in inhumane conditions.

“Despite the critical role these flights play in the removal system – in many instances, serving as the mechanism for deportation – ICE Air remains shrouded in secrecy,” said the lawsuit, filed in Los Angeles by the American Civil Liberties Union Foundation of Southern California. “This secrecy has masked responsibility for serious abuses and danger on ICE Air flights.”

During his campaign, Trump promised to increase deportations starting on “day one” of his administration, though he has provided few details about how he would execute that plan. The comments sent advocates for immigrants scrambling for details about the existing state of the deportation system so that they could protect immigrants and inform U.S. taxpayers about its cost.

“We’ve been preparing for a mass detention and deportation agenda for the last nine months,” said Kyle Virgien, a senior staff attorney at the ACLU. “Now that Trump is the president-elect, it’s become apparent that this is a fight that we’re going to need to have.”

ICE spokesman Mike Alvarez said Monday that the agency does not comment on pending litigation.

Karoline Leavitt, spokeswoman for the Trump-Vance transition team, reaffirmed Monday that Trump intends to “marshal every federal and state power necessary to institute the largest deportation operation of illegal criminals, drug dealers, and human traffickers in American history while simultaneously lowering costs for families.”

Trump made similar threats to deport immigrants during his first term from. Partly because of resistance from Democrat-led cities and towns, his administration deported fewer than 1 million of the estimated 11 million people living in the country illegally, according to the Migration Policy Institute, a Washington think tank.

During Trump’s first term, the ACLU proved to be his arch-nemesis in court, filing approximately 430 legal challenges against his policies on immigration and other issues. On immigration, lawyers fought Trump’s efforts to restrict access to asylum and led a major case that halted his forced separation of migrant parents and children at the U.S.-Mexico border.

Trump adviser Stephen Miller was so frustrated by the nonprofit that he founded a conservative legal organization, America First Legal, after Trump lost the 2020 election to Joe Biden and called it “the long-awaited answer to the ACLU.”

In the lawsuit filed Monday, the ACLU said it requested information in August about ICE Air operations from Jan. 1, 2023, to the present.

ICE had 30 days to respond under the federal Freedom of Information Act, the lawsuit said. Despite invoking a 10-day extension, ICE has not provided the requested information, leading the ACLU to allege the agency is in violation of federal law.

Lawyers asked the court to order ICE to release the information immediately and to block the agency from withholding future records.

Over the past few decades, the lawsuit said, deportation flights have shifted from a mostly government-run operation under the U.S. Marshals Service to “a sprawling and opaque network of flights on privately-owned aircraft chartered by ICE Air.”

In 2023, the government of Colombia temporarily suspended deportation flights after discovering that ICE shackled mothers traveling with children, calling the practice cruel and degrading.

In another case, ICE tried to deport 92 men and women to Somalia in December 2017. The plane ended up stuck on a tarmac in Senegal for 23 hours and then returned to the United States, according to court records. The detainees were shackled during the 48-hour journey.

The Department of Homeland Security Inspector General’s office criticized the agency in a 2023 report that said ICE had budgeted nearly $800 million for air and land transport from October 2019 through April 2022, but did not consistently monitor the companies’ performance and spending.

Monday’s lawsuit is the fourth FOIA that the ACLU and its affiliates have filed in recent months seeking information about deportation and detention operations, and it is the first since Trump was elected.

“The Freedom of Information Acts requires federal agencies to disclose information requested by the public,” said Sophie Mancall-Bitel, a partner at Mayer Brown LLP, a law firm that is supporting the lawsuit. “It’s more important than ever that we understand what federal resources could be used to forcibly remove people from the United States.”

ICE operated 1,178 removal flights last fiscal year, sending more than 142,000 people to approximately 170 countries. Nearly half had been charged, or convicted, of a crime.