U.S. District Judge James E. Boasberg said he needed to issue his order immediately because the government already was flying migrants it claimed were newly deportable under President Donald Trump’s proclamation to be incarcerated in El Salvador and Honduras. El Salvador already agreed this week to take up to 300 migrants that the Trump administration designated as gang members.

“I do not believe I can wait any longer and am required to act,” Boasberg said during a Saturday evening hearing in a lawsuit brought by the ACLU and Democracy Forward. “A brief delay in their removal does not cause the government any harm,” he added, noting they remain in government custody but ordering that any planes in the air be turned around.

The ruling came hours after Trump claimed the Venezuelan gang Tren de Aragua was invading the United States and invoked the Alien Enemies Act of 1798, a wartime authority that allows the president broader leeway on policy and executive action to speed up mass deportations.

The act has only ever been used three times before, all during wars. Its most recent application was during World War II, when it was used to incarcerate Germans and Italians as well as for the mass internment of Japanese-American civilians.

In a proclamation released just over an hour before Boasberg’s hearing, Trump contended that Tren de Aragua was effectively at war with the United States.

“Over the years, Venezuelan national and local authorities have ceded ever-greater control over their territories to transnational criminal organizations, including TdA,” Trump’s statement reads. “The result is a hybrid criminal state that is perpetrating an invasion of and predatory incursion into the United States, and which poses a substantial danger to the United States.”

The order could let the administration deport any migrant it identifies as a member of the gang without going through regular immigration proceedings, and also could remove other protections under criminal law for people the government targeted.

In a statement Saturday night, Attorney General Pam Bondi slammed Boasberg’s stay on deportations. “This order disregards well-established authority regarding President Trump’s power, and it puts the public and law enforcement at risk,” Bondi said.

The Tren de Aragua gang originated in a prison in the South American country and accompanied an exodus of millions of Venezuelans, the overwhelming majority of whom were seeking better living conditions after their nation’s economy came undone last decade. Trump and his allies have turned the gang into the face of the alleged threat posed by immigrants living in the U.S. illegally and formally designated it a “foreign terrorist organization” last month.

Authorities in several countries have reported arrests of Tren de Aragua members, even as Venezuela’s government claims to have eliminated the criminal organization.

The government said Trump actually signed the proclamation on Friday night. Immigration lawyers noticed the federal government suddenly moving to deport Venezuelans who they would not otherwise have the legal right to expel from the country, and scrambled to file lawsuits to block what they believed was a pending proclamation.

Boasberg issued an initial order at 9:20 a.m. Saturday blocking the Trump administration from deporting five Venezuelans named as plaintiffs in the ACLU suit who were being detained by the government and believed they were about to be deported. The Trump administration appealed that order, contending that halting a presidential act before it has been announced would cripple the executive branch.

If the order were allowed to stand, “district courts would have license to enjoin virtually any urgent national-security action just upon receipt of a complaint,” the Justice Department wrote in its appeal.

Boasberg then scheduled the afternoon hearing on whether to expand his order to all people who could be targeted under Trump’s declaration.

Deputy Assistant Attorney General Drew Ensign contended that the president had broad latitude to identify threats to the country and act under the 1798 law. He noted the U.S. Supreme Court allowed President Harry Truman to continue to hold a German citizen in 1948, three years after World War II ended, under the measure.

“This would cut very deeply into the prerogatives of the president,” Ensign said of an injunction.

But Lee Gelernt of the ACLU contended that Trump didn’t have the authority to use the law against a criminal gang rather than a recognized state. Boasberg said precedent on that question seemed tricky but that the ACLU had a reasonable chance of success on those arguments, and so the order was merited.

Boasberg halted deportations for those in custody for up to 14 days, and scheduled a Friday hearing in the case.

The flurry of litigation shows the significance of Trump’s declaration, the latest step by the administration to expand presidential power. Ensign argued that, as part of its reaction to the Sept. 11, 2001 attack, Congress had given the president power to delegate “transnational” organizations threats on the level of recognized states. And Gelernt warned that the Trump administration could simply issue a new proclamation to use the Alien Enemies Act against another migrant gang, like MS-13, which has long been one of Trump’s favorite targets.