The U.S. Supreme Court on Friday maintained a block on President Donald Trump's deportation efforts targeting Venezuelan migrants under a rarely invoked wartime statute from 1798, emphasizing the administration’s lack of proper legal procedure.

In a brief, unsigned opinion, the Court agreed with attorneys from the American Civil Liberties Union (ACLU), who argued the Trump administration violated migrants’ constitutional rights by not providing adequate notice or sufficient opportunity to challenge deportations. The administration was criticized for giving only around 24 hours of advance notice without clear instructions on how detainees could contest their removal.

"Under these circumstances, notice roughly 24 hours before removal, devoid of information about how to exercise due process rights to contest that removal, surely does not pass muster," the Supreme Court stated.

Trump reacted sharply to the decision, posting online, "This is a bad and dangerous day for America!" He expressed frustration that the ruling would mandate a prolonged and costly legal process, potentially allowing criminal migrants to remain in the country indefinitely. The President further claimed the decision would encourage more illegal immigration.

The deportations at issue involved migrants allegedly linked to the Venezuelan criminal organization Tren de Aragua, which the State Department designates as a foreign terrorist group. The migrants were slated for deportation to a maximum-security facility in El Salvador under an agreement costing the U.S. government $6 million.

Lawyers representing the detainees argued the Trump administration's actions violated the Supreme Court's earlier orders demanding proper notice and opportunity for judicial review. Lee Gelernt, lead counsel for the ACLU, called the Court's ruling a "powerful rebuke" to the administration's attempt to rapidly deport migrants under a law historically reserved for wartime emergencies.

Conservative Justices Samuel Alito and Clarence Thomas publicly dissented from Friday’s ruling. Justice Alito wrote separately, expressing skepticism over the Court's jurisdiction in the current procedural stage and questioned whether granting relief to detainees as a collective was legally appropriate.

The Supreme Court has now directed the 5th U.S. Circuit Court of Appeals to clarify precisely what due process procedures must be followed for these deportations. However, the justices emphasized that the administration could still pursue removals using alternative immigration laws.