New Jersey is joining 18 other states in suing the Trump administration’s effort to alter a federal agreement that limits how long immigrant children can be kept in detention.

In the complaint, the states allege the Trump administration is violating a 1997 agreement known as the Flores settlement, which says immigrant children must be kept in the least restrictive setting and generally shouldn’t spend more than 20 days in detention.

The U.S. Department of Homeland Security said last week it would create new regulations on how migrant children are treated. The administration wants to remove court oversight and allow families to stay in detention longer than 20 days.

“For over two decades, across administrations, the federal government followed legal protections to ensure detained immigrant children are released as quickly possible,” said Attorney General Gurbir Grewal. “The Department of Homeland Security’s new rule strips away those protections, allowing for the prolonged detention of children in conditions that are harmful to their mental and physical health. This new rule violates the law, and we’re going to court to stop it.”

Other states joining the lawsuit are California, Connecticut, Delaware, Illinois, Maine, Maryland, Michigan, Minnesota, Nevada, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, Washington and the District of Columbia.