Washington (AFP) - The US Supreme Court, in a dramatic nighttime intervention Saturday, paused President Donald Trump’s unprecedented use of an obscure law to deport Venezuelan migrants without due process.

The emergency ruling, delivered in two terse paragraphs, noted that two of the most conservative of the nine justices had dissented.

The order temporarily prevents the government from continuing to expel migrants under the 1798 Alien Enemies Act – last used to round up Japanese-American citizens during World War II.

Trump invoked the law last month to deport Venezuelans to a notorious prison in El Salvador.

The unusual decision was triggered by imminent plans late Friday to expel dozens more Venezuelans under the Act, meaning they would have been deported with next to no ability to hear evidence against them or challenge their cases.

The court said “the government is directed not to remove any member of the putative class of detainees from the United States until further order.”

Trump justifies summary expulsions – and the detention of people in El Salvador – by insisting that he is cracking down on violent Venezuelan criminal gangs now classified by the US government as terrorists.

But the policy is fueling opposition concerns that the Republican is ignoring the US constitution in a broader bid to amass power.

The row over the Alien Enemies Act comes amid muscular assaults by the administration on big law firms, Harvard and other universities, and major independent media outlets.

The American Civil Liberties Union, which took the lead in seeking to halt Friday’s planned deportations, welcomed the Supreme Court ruling.

“These men were in imminent danger of spending their lives in a horrific foreign prison without ever having had a chance to go to court. We are relieved that the Supreme Court has not permitted the administration to whisk them away the way others were just last month,” lead attorney Lee Gelernt said.

- Tattoos and due process -

Trump’s election last November was won in large part on his aggressive promises to combat what he has repeatedly claimed is an “invasion” of violent migrants.

While there is no evidence to support the narrative of the United States being “invaded,” Trump’s rhetoric about rapists and murderers descending on suburban homes resonated with swaths of voters who have long been concerned about high levels of illegal immigration.

Trump has sent troops to the Mexican border, imposed tariffs on Mexico and Canada for allegedly not doing enough to stop illegal crossings, and designated narco-gangs like Tren de Aragua and MS-13 terrorist groups.

However, Democrats and civil rights groups have expressed alarm at an erosion of constitutional rights.

Under Trump’s use of the Alien Enemies Act – previously seen only during the War of 1812, World War I and World War II – migrants have been accused of gang membership and sent to El Salvador without ability to go before a judge or being charged with a crime.

Attorneys for several of the Venezuelans already deported had said their clients were targeted largely on the basis of their tattoos.

In the most publicized case, Maryland resident Kilmar Abrego Garcia was deported last month to the infamous El Salvador mega-prison without charge.

The Trump administration said he had been included in a bigger batch of deportees due to an “administrative error” and a court ruled that it must facilitate his return.

However, Trump has since doubled down, insisting that Abrego Garcia is in fact a gang member, including posting an apparently doctored photo on social media Friday that showed MS-13 on his knuckles.

Most of the deported migrants are currently held in El Salvador’s maximum security Terrorism Confinement Center (CECOT), a mega-prison southeast of the capital San Salvador with capacity for 40,000 prisoners.

Inmates are packed in windowless cells, sleep on metal beds with no mattresses, and are forbidden visitors.