In the most comprehensive decision to date against a significant aspect of the Republican president’s harsh immigration crackdown, a U.S. judge on Thursday barred President Donald Trump’s administration from using a wartime law from the 18th century to deport some Venezuelan migrants.

U.S. District Judge Fernando Rodriguez of Brownsville, Texas, claimed in a 36-page ruling that the Trump administration had overreached itself by using the Alien Enemies Act to expedite the deportations of suspected members of the Venezuelan gang Tren de Aragua. The gang is classified as a terrorist organization by the government.

There are several legal challenges to Trump’s mid-March proclamation that used the 1798 law to support his quick deportations. A Colorado judge ruled last week that the administration must give migrants at least 21 days to contest their possible removals in court, temporarily stopping the administration from deporting migrants detained in their districts under the Alien Enemies Act.

Rodriguez’s decision was more extensive. During his first term in office, Trump appointed the judge, who permanently barred the administration from deporting Venezuelans held in the Southern District of Texas according to the law.

Writing that Tren de Aragua’s actions in the United States did not amount to a “invasion” or “predatory incursion” that would justify the use of the Alien Enemies Act, his ruling was also the first to categorically reject Trump’s invocation of the law.

Rodriguez, whose district includes the detention facility from which at least 137 Venezuelan men were deported to El Salvador on March 15, just after Trump invoked the law, wrote, “The President’s invocation of the AEA through the Proclamation exceeds the scope of the statute and, as a result, is unlawful.”

Trump’s election victory, according to White House spokesman Kush Desai, has given him the authority to “deport terrorist illegal aliens.”

“The Trump administration is committed to unapologetically using every lever of power endowed to the executive branch by the Constitution and Congress to deliver on this mandate, and we are confident that we will ultimately prevail,” Desai stated.

Rodriguez’s decision could be appealed by the administration to the Fifth U.S. Circuit Court of Appeals, which is widely regarded as the most conservative of the nation’s twelve appellate courts.

Most famously, during World War Two, the Alien Enemies Act was used to intern and deport individuals of German, Italian, and Japanese ancestry.

Congress did not intend for the law to be applied the way Trump has, according to Lee Gelernt, an attorney with the American Civil Liberties Union who is defending the Venezuelan migrants.

“The court ruled that the president cannot unilaterally invoke an 18th-century wartime authority in peacetime after merely declaring an invasion of the United States,” Gelernt said.

Many of the Venezuelan men who were deported under the law last month have lawyers and relatives who deny they were members of Tren de Aragua. They also claim the deportees were not given the opportunity to challenge the administration’s claims.

In response to those deportations, the U.S. Supreme Court decided on April 7 that the Trump administration must allow migrants to challenge any further deportations under the Alien Enemies Act in court.

In response, the ACLU challenged legal deportations in courts across the nation where Venezuelan migrants were being held.

Last week, the civil liberties group also requested that U.S. District Judge James Boasberg of Washington order the Trump administration to make it easier for the migrants who have already been deported to return to El Salvador, where the United States is paying President Nayib Bukele’s government $6 million to hold them at the Terrorism Confinement Center in the Central American nation.

Boasberg hasn’t made a decision yet.