A federal judge on Saturday temporarily blocked any deportations that would occur under U.S. President Donald Trump's use of a little-used wartime law to expedite the expulsion of alleged members of the Venezuelan gang Tren de Aragua.

Hours earlier, Trump invoked the Alien Enemies Act of 1798 against the group, saying the United States was facing an "invasion" from a criminal organization that has been linked to kidnapping, extortion, organized crime and contract killings.

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Judge James Boasberg issued a temporary restraining order for 14 days. Boasberg said the act "does not provide a basis for the president's proclamation given that the terms invasion, predatory incursion really relate to hostile acts perpetrated by any nation and commensurate to war."

In invoking the act, Trump said members of the gang were "conducting irregular warfare and undertaking hostile actions against the United States" with the goal of destabilizing the nation.

The act, which has only been used in times of war, could allow the president to bypass the due process rights of migrants categorized as threats and rapidly deport them.

While the proclamation was released by the White House on Saturday, the wording suggests Trump signed it on Friday.

"This proclamation is as lawless as anything the Trump administration has done," Lee Gelernt, a lawyer with the American Civil Liberties Union, who argued for the order in a hearing on Saturday, told Reuters in an interview.

"We are on very dangerous ground when the administration is going to try to use wartime authority, when we're at peace, for immigration purposes or any other non-military purpose."

Attorney General Pam Bondi said Boasberg "had supported Tren de Aragua terrorists over the safety of Americans" in his ruling. "This order disregards well-established authority regarding President Trump's power, and it puts the public and law enforcement at risk," she said in a statement.

Under Trump's proclamation, all Venezuelan citizens 14 years of age or older who are determined to be members of the gang, are within the United States and are not naturalized or lawful permanent residents of the country are "liable to be apprehended, restrained, secured, and removed as Alien Enemies."

The Alien Enemies Act is best known for its use to justify internment camps for people of Japanese, German and Italian descent during World War Two.

Civil rights groups and some Democrats have criticized the idea of reviving it to fuel mass deportations.

The Trump administration in February designated Tren de Aragua, the Sinaloa Cartel and six other criminal groups as global terrorist organizations.

Saturday's directive said that Tren de Aragua "has engaged in and continues to engage in mass illegal migration to the United States to further its objectives of harming United States citizens."

LAWSUITS AND CRITICISM

Trump made the threat posed by the gang a regular feature of his campaign speeches as evidence of what he called a spike in "migrant crime." Numerous studies show immigrants do not commit crimes at higher rates than native-born Americans.

Immigration advocacy groups and Democrats ripped Trump's decision.

"Invoking the Alien Enemies Act, an extraordinary wartime power with a shameful history, to arbitrarily detain and deport immigrants is bigoted, dangerous, and profoundly unjust," said New York Attorney General Letitia James.

William Vasquez, a immigration lawyer in North Carolina, posted on social media that this is the first time the act "has been applied against migrants from a country with which the U.S. is not at war."

Earlier on Saturday, Boasberg had temporarily blocked the U.S. government from deporting five Venezuelans after two non-profit groups sued, saying invocation of the act would be illegal as it has only been "a power invoked in a time of war, and plainly only applies to warlike actions."

The court granted a temporary restraining order, stopping the government from deporting them for 14 days. The ACLU said the Venezuelans are seeking asylum and have been misidentified as being part of Tren de Aragua.

The White House did not immediately respond to a request for comment. Court papers show the government has appealed the judge's first temporary restraining order.

Trump, a Republican, returned to the White House on January 20 vowing to deport millions of immigrants living in the U.S. illegally. But his initial deportations have lagged behind those of his Democratic predecessor Joe Biden, who faced high levels of illegal immigration and rapidly deported many recent border crossers.

Trump has taken an array of actions to step up immigration enforcement, sending additional troops to the U.S.-Mexico border and reassigning federal agents to help track down immigration offenders.

But his administration has had to contend with backed-up immigration courts and limited detention space.