The Trump administration announced that it would block nearly all migrants from seeking asylum Monday, in a new rule that legal experts say violates both domestic and international law. The ACLU has already vowed to challenge the rule in court. It would deny asylum to any migrant who failed to apply for protection in another country they passed through on the way to the U.S. border—including children traveling alone. If enacted, it would effectively block people from Honduras, El Salvador and Guatemala from seeking refuge in the United States. Trump announced the plan without Guatemala and Mexico’s agreement.