President Donald Trump invoked rarely used war powers in a bid to deport foreign nationals that the federal government deems to be members of the Venezuelan gang Tren de Aragua.

Trump’s proclamation — which was released by the White House Saturday afternoon but signed on Friday — relies on the Alien Enemies Act of 1798, which is meant to quickly remove foreigners during wartime or invasion, and comes hours after a preemptive order from a federal judge barred five Venezuelan nationals from being deported immediately.

It’s the latest sweeping executive action from the White House designed to speed up Trump’s efforts to deport millions of undocumented immigrants from the country.

“I find and declare that TdA is perpetrating, attempting, and threatening an invasion or predatory incursion against the territory of the United States,” Trump wrote in his declaration.

The order landed amid a scramble in multiple federal courts by foreign nationals who sued to block imminent deportations they were told were being initiated pursuant to Trump’s anticipated order.

The order directs Attorney General Pam Bondi to sign a letter within 60 days declaring this the policy of the U.S., and for the letter to be sent to every judge, including the justices on the Supreme Court, as well as the governor of every state.

Every immigrant that meets the description outlined in the order “are subject to immediate apprehension, detention, and removal.” It is not clear how many members of Tren de Aragua are currently in the United States — or how the government will make such designations.

Trump repeatedly suggested during his campaign he may turn to the Alien Enemies Act to aid his mass deportation plans, a promise he reiterated on Inauguration Day. The president said on Jan. 20 that he would use the wartime law to “direct our government to use the full and immense power of federal and state law enforcement to eliminate the presence of all foreign gangs and criminal networks bringing devastating crime to U.S. soil, including our cities and inner cities.”

He also moved last month to designate eight Latin American cartels, including Tren de Aragua, as foreign terrorist organizations.

“We’ll be reading a lot of stories tomorrow about what we’ve done with them,” Trump said at the Justice Department on Friday, speaking about Tren De Aragua. “You’ll be very impressed, and you feel a lot safer, because they are a vicious group.”

Hours before the president’s proclamation was published online, U.S. District Judge James Boasberg issued the urgent ruling blocking the deportations. He cited “exigent circumstances,” issuing his order just hours after a lawsuit was filed on behalf of five Venezuelan men who say they have been cued up for deportation within hours or days as a result of Trump’s expected decision to invoke the Alien Enemies Act.

Boasberg, the chief judge for the federal district court in Washington, D.C., also called for a hearing Saturday afternoon on the lawsuit’s effort to ensure anyone else targeted by Trump’s expected invocation is protected from immediate deportation.

The lawsuit, filed by Democracy Forward and the ACLU, emphasizes that the Alien Enemies Act has only been invoked during wartime — the War of 1812, World War I and World War II. The order by Boasberg was issued with unusual urgency, before the Trump administration had a chance to respond.

But the administration quickly filed with the D.C. Circuit Court of Appeals, asking Saturday afternoon for an emergency stay of Boasberg’s ruling. In their motion, the administration said that the argument over the use of the Alien Enemies Act was hypothetical — which is no longer the case — and “fundamentally a political question to be resolved by the President.”

Attorneys for the five Venezuelans say the order could subject “countless Venezuelans” to “imminent risk of deportation without any hearing or meaningful review.” The five men who filed the initial lawsuit say they were informed by immigration authorities to expect deportation as soon as Saturday night.

Boasberg’s Saturday order prevents any of the five plaintiffs from being deported for 14 days.

The centuries-old law allows the government to arrest, detain and deport undocumented migrants over the age of 14 who come from countries threatening an “invasion or predatory incursion” of the United States.

Those targeted under the wartime law would be swiftly deported and would not be allowed to have an asylum interview or an immigration court hearing. They would instead be detained and deported with little due process.

Since he took office, federal judges have issued a handful of rulings to slow or halt components of Trump’s immigration crackdown amid a blitz of lawsuits claiming aspects of those efforts ran afoul of the law or constitution. Judges have ordered the administration to lift a total freeze on refugee admissions and blocked enforcement actions at some places of worship.

Most notably, several federal courts have issued nationwide blocks on Trump’s effort to redefine the Constitution’s birthright citizenship clause to exclude children of undocumented immigrants.

“There is so much urgency here, and so much harm at stake,” said ACLU attorney Lee Gelernt, who is representing the Venezuelan nationals, at a Saturday hearing. “The government appears to be moving planes very rapidly, our understanding is that planes are going right now.”

On Saturday afternoon, flight tracking databases showed three flights scheduled to depart from the Harlingen, Texas, airport on planes operated by a company that contracts with Immigration & Customs Enforcement to do deportation flights. Two of the aircraft registered flight plans headed for Honduras and one for El Salvador.

Video posted online Saturday showed a bus approaching the airport accompanied by law enforcement vehicles. According to the post, immigration lawyer Jaime Diez recorded the images of immigrants from the El Valle detention center in Raymondville, Texas being transferred for deportation.

Earlier Saturday, Diez won an order from a federal judge in Brownsville barring the deportation of Venezuelan Daniel Zacarias Matos. According to a court filing, Zacarias Matos was told Friday he was being taken to the airport to be deported “due to an order from the President,” but the flight didn’t take off because “it did not pass an inspection.”

One of the Honduras flights took off during a break in Boasberg’s hearing, the databases showed. The status of the other two flights is unclear.

Ali Bianco and Josh Gerstein contributed to this report.