Attorney General William Barr issued an order Tuesday limiting immigration judges’ power to release asylum seekers from detention on bond, marking another step in the Trump administration’s efforts to keep migrants from coming to the United States.

Barr’s order is likely to strain the immigrant detention system, already handling high numbers of migrants, especially families and unaccompanied children, arriving at the southern border. Under the ruling, certain immigrants cannot be released on bond and instead must remain in detention unless the Department of Homeland Security chooses to release them.

The order said that migrants who cross the border illegally and are put in expedited removal proceedings remain subject to mandatory detention, even if they are transferred to full proceedings for seeking relief to remain in the U.S. Such a transfer would happen after an interview in which someone seeking asylum has established a credible fear of persecution or torture if returned to their home country. The ruling will go into effect in 90 days.

The ruling does not apply to children who are apprehended with their parents or alone. Families are currently released from detention after about three weeks under the Flores Settlement, which limits how long children can remain locked up ― although the administration has suggested it wants to give parents the decision to either remain together in detention or be separated so their children can be released. Unaccompanied minors detained by border authorities are transferred to Department of Homeland Security custody.

Barr’s ruling said it does not take into account whether detaining migrants indefinitely during proceedings is constitutional. But immigration rights advocates and lawyers believe the decision will deny asylum seekers their basic rights. The American Civil Liberties Union is planning to sue the Justice Department over the decision.

“This is the Trump administration’s latest assault on people fleeing persecution and seeking refuge in the United States,” Omar Jadwat, director of the ACLU’s Immigrants’ Rights Project, said Tuesday in a statement. “Our Constitution does not allow the government to lock up asylum seekers without basic due process. We’ll see the administration in court.”