FILE - In this June 26, 2018, file photo, vehicles leave the Port Isabel Detention Center, which holds detainees of the U.S. Immigration and Customs Enforcement in Los Fresnos, Texas. The Trump administration said Sept. 6, it is abandoning a longstanding court settlement that limits how long immigrant children can be kept locked up, and it is proposing new regulations that would let the government detain families until their immigration cases are decided. (AP Photo/David J. Phillip, file)
FILE - In this June 26, 2018, file photo, vehicles leave the Port Isabel Detention Center, which holds detainees of the U.S. Immigration and Customs Enforcement in Los Fresnos, Texas. The Trump administration said Sept. 6, it is abandoning a longstanding court settlement that limits how long immigrant children can be kept locked up, and it is proposing new regulations that would let the government detain families until their immigration cases are decided. (AP Photo/David J. Phillip, file) Credit: David J. Phillip

Washington — The Trump administration took the first official step on Thursday toward withdrawing from a court agreement that limits the government’s ability to hold minors in immigration jails, a move advocates say could lead to a rapid expansion of detention facilities and more time in custody for children.

The changes proposed by the Department of Homeland Security and the Department of Health and Human Services would terminate the Flores Settlement Agreement, the federal consent decree that has shaped detention standards for underage migrants since 1997.

The maneuver is almost certain to land the administration back in court, where U.S. District Court Judge Dolly Gee, who oversees the agreement, has rejected attempts to extend the amount of time migrant children can be held with their parents beyond the limit of 20 days. The new rules would lift those restrictions and allow the government to detain migrant children until their cases have been fully adjudicated.

DHS officials say the change would not undermine the protections mandated by the court agreement, but rather fully implement them as a set of formal policies to ensure migrant children “are treated with dignity, respect and special concern for their particular vulnerability as minors.”

“Today, legal loopholes significantly hinder the Department’s ability to appropriately detain and promptly remove family units that have no legal basis to remain in the country,” DHS Secretary Kirstjen Nielsen said in a statement. “This rule addresses one of the primary pull factors for illegal immigration and allows the federal government to enforce immigration laws as passed by Congress.”

The proposal sets up a new immigration battle in court, and comes less than three months after the Trump administration’s short-lived attempt to halt an increase in illegal migration by separating children from parents who entered unlawfully. The practice widely was condemned and forced the administration to reverse course and regroup.

The changes proposed by the administration would allow U.S. Immigration and Customs Enforcement to expand its family detention facilities in order to keep parents and children together in custody for lengthier periods. ICE currently has three such facilities, which it calls “family residential centers,” with a combined capacity of about 3,000 beds.

But those facilities almost always are full, and the limitations on child detention under the Flores settlement have been a disincentive to build more. The Trump administration has directed the Pentagon to identify sites where new detention centers could be added with space for 12,000 additional beds.

The 1997 Flores Settlement Agreement resulted from a class-action lawsuit over the treatment of migrant children in federal custody, and has required the government to hold migrant children in the least-restrictive setting possible. It also mandates that those facilities are licensed, but while states typically license child care facilities, none issue licenses to family detention centers.