A rare trial began Monday in a class action challenging the placement of unauthorized migrant children in adult detention facilities once they turned 18.

The bench trial, expected to last three weeks, comes in a case brought by Kirkland & Ellis and the National Immigrant Justice Center against the U.S. Department of Homeland Security and its unit, U.S. Immigration and Customs Enforcement. Plaintiffs allege that government officials routinely violate the federal Trafficking Victims Protection Reauthorization Act, which, under a 2013 amendment, requires that authorities place unaccompanied migrant children who turn 18 in the "least restrictive setting available."

"The plaintiffs are a class of those individuals who are currently incarcerated in county jails and adult detention facilities across the country," said Stephen Patton, of counsel in Chicago at Kirkland & Ellis, who is trying the case pro bono with firm partner Tia Trout-Perez, in Washington, D.C., and the National Immigrant Justice Center. "Under federal law, ICE has to make a determination where to place these kids, who have just aged out. That includes placing them in adult detention, or some other less restrictive alternative, which is where this statute comes into play."

In addition to their agencies, former ICE Acting Director Thomas Homan and former Homeland Security Secretary Kirstjen Nielsen are defendants in the case.

A representative of the Homeland Security Department did not respond to a request for comment. In court documents, government lawyers insisted that ICE has a nationwide policy that complies with the amended statute, such as completing an "age-out review worksheet."

"This is a blatant attempt to compel agency action which is not unlawfully withheld because it is not required in the first instance," they wrote in pretrial documents filed last month. "Rather, plaintiffs ask the court to re-write the statute in accordance with plaintiffs' policy preferences."

The case, which seeks injunctive relief, is the latest to challenge immigration policies under President Donald Trump.

"There definitely was a pretty significant increase in the rate at which these young people were detained by ICE starting after the 2016 election and early 2017 with the new administration," Patton said. "So, overall, there is a correlation between the increased detention of these young people and the new administration, but when that increase occurred, it varies by field office."

The named plaintiffs are two migrant teenagers—a girl from Honduras and a boy from Guatemala—who entered the United States as minors without their parents. The boy, Wilmer Garcia Ramirez, escaped poverty, neglect and "deplorable" working conditions at a coffee plantation, while the girl, Sulma Hernandez Alfaro, fled an uncle who threatened to kill her.

Initially, both fell under the direction of the U.S. Department of Health and Human Service's Office of Refugee Resettlement, which has authority over the detention of minors. Immigration authorities transferred them to ICE facilities in Arizona and Texas once they turned 18.

That violated the federal trafficking victims statute, which requires the "least restrictive" alternative, such as staying with a family friend or sponsor, or a group home, or released on bond.

"Instead, ICE automatically places unaccompanied immigrants who have turned 18 into adult detention without considering or making available the least restrictive (or other) alternatives," says the complaint, filed in 2018.

The case estimated the class to be thousands of migrants.

"We have a data set from 2016 through May 2019 and within that data set around 4,700 kids who aged out, and of that 4,700, more than 50% were detained," said Kate Melloy Goettel, associate director of litigation at National Immigrant Justice Center.

The trial is taking place before U.S. District Judge Rudolph Contreras of the District of Columbia. Last year, Contreras granted a preliminary injunction to the lead plaintiffs and refused to dismiss the class action, despite immigration authorities releasing both of them from detention. He also certified the class, concluding that the case was about a "single alleged practice" involving more than just the named plaintiffs.

"Here, plaintiffs explain that, like the other members of the putative class, the named plaintiffs are former unaccompanied minors who, upon reaching their respective 18th birthdays, were transferred from ORR custody to DHS and placed in adult facilities," he wrote.