A federal appeals court ruled late on Tuesday that the Trump administration cannot use the Alien Enemies Act to deport Venezuelan gang members, blocking a central part of the president’s strategy to combat Tren de Aragua.

President Donald Trump has relied on the 18th-century wartime law to deport alleged members of the gang. The ruling came as a surprise to many, given that the three-judge 5th U.S. Circuit Court of Appeals is one of the most conservative appeals courts in the U.S. The George W. Bush-appointed U.S. Circuit Judge Leslie Southwick and Joe Biden-appointed Irma Carrillo Ramirez ruled against Trump, while the Trump-appointed Andrew Oldham dissented.

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The majority opinion disregarded the administration’s logic, saying they “found no invasion or predatory incursion” in this case.

“A country’s encouraging its residents and citizens to enter this country illegally is not the modern-day equivalent of sending an armed, organized force to occupy, to disrupt, or to otherwise harm the United States,” the majority wrote.

Oldham scorched his colleagues in a lengthy dissent, arguing that the ruling was bleeding into the president’s preeminent role over foreign affairs and national security.

“The majority’s approach to this case is not only unprecedented—it is contrary to more than 200 years of precedent,” Oldham wrote.

He also warned that the majority ruling risks turning federal judges into “robed crusaders who get to playact as multitudinous Commanders in Chief.”

FIRST FEDERAL JUDGE APPROVES TRUMP’S USE OF ALIEN ENEMIES ACT FOR DEPORTATIONS

The Trump administration is almost certain to appeal the matter to the Supreme Court. The nation’s highest court previously ruled that Trump could deport people under the act, but that they had to be able to argue their case in court first.

Trump’s usage of the AEA has seen a seesaw of opinions in the U.S. court system. Judge Stephanie Haines of the U.S. District Court for the Western District of Pennsylvania ruled in favor of Trump back in May, agreeing with the administration’s logic.