The new regulation affects anyone who travels through a third country before seeking asylum in the US.

Marco Ugarte / AP Central Americans traveled through Mexico as part of a thousands-strong caravan hoping to reach the US border in November 2018.

The US will end asylum protections for Central Americans and others who cross through Mexico to reach the southern border, the Trump administration announced Monday, a sweeping, unprecedented move that will quickly be challenged in court. The new move, which bars asylum for any individual who crosses through a third country but does not apply there for protection before reaching the US southern border, takes effect Tuesday in the form of a regulatory change. It becomes the latest in a series of attempts by the Trump administration to actively deter asylum-seekers from reaching the border. The details of the plan and efforts to implement it were first reported by BuzzFeed News in May, and experts say it would keep hundreds of thousands of people fleeing violence from entering the US. “With one regulation the US is nearly entirely turning its back on this asylum flow,” Sarah Pierce, an analyst at the Migration Policy Institute, told BuzzFeed News. Multiple Department of Homeland Security officials who spoke with BuzzFeed News voiced concerns about the administration’s move. “It’s fucked up,” one official said. “There’s a reason people apply for asylum in the US — we have a robust asylum system. Other countries on the route to the southern border don’t.”

Rodrigo Abd / AP

Another said it would be blocked in court. “Flatly inconsistent with our treaty obligations. Flies in the face of decades of case law. Destined to be enjoined and or struck down immediately,” the official said. Another DHS official said the move was not only mistaken, but it would backfire on the administration. “This administration continues to pervert the 1980 Refugee Act and its later amendments by passing regulations that burden its own employees with overly cumbersome, ill-conceived new ‘standards,’” the official said. “This rule will affect all those who reach our southern land border but may have fled from anywhere in the world. It does nothing to fix our broken immigration system, which is at its breaking point because of the administration’s mismanagement.”

At a press conference, Mexican Foreign Minister Marcelo Ebrard told reporters Monday that he did not agree with the measure limiting asylum for those fleeing their countries.

Administration officials have been working on the plan for weeks, considering it a potential solution to the high rate of families crossing the border. “Until Congress can act, this interim rule will help reduce a major ‘pull’ factor driving irregular migration to the United States and enable DHS and [the Department of Justice] to more quickly and efficiently process cases originating from the southern border, leading to fewer individuals transiting through Mexico on a dangerous journey,” said acting DHS Secretary Kevin McAleenan. But congressional staffers who were informed of the policy Monday morning raised questions about its legality, according to a source with knowledge of the conversation.

Advocates said they would move to sue immediately.

Lee Gelernt, deputy director of the Immigrants’ Rights Project of the American Civil Liberties Union, said the group would immediately sue. “The Trump administration is trying to unilaterally reverse our country’s legal and moral commitment to protect those fleeing danger. This new rule is patently unlawful and we will sue swiftly,” he said. The ACLU previously filed a lawsuit over the administration’s attempt to ban asylum for those who crossed the border without authorization. The policy was later blocked in federal court and has since not been implemented.

Oliver De Ros / AP