As of Wednesday, the Trump administration is officially allowed to enforce a new policy denying asylum to migrants at the southern border who have not sought protection from the US or other countries.

A US district judge had blocked the policy from going into effect nationwide — days after it was unveiled in July — but the Supreme Court decided to reverse the decision in a brief order late in the day.

Associate Justices Ruth Bader Ginsburg and Sonia Sotomayor both dissented from the high court’s ruling, which came after a federal appeals court panel initially chose to uphold the blocking in district court.

Solicitor General Noel Francisco argued Wednesday that the asylum rule — which is meant to bar immigrants from entering the country without seeking protection from the US or nations they travel through — was supposed to keep out people “who declined to request protection at the first opportunity.”

“It alleviates a crushing burden on the U.S. asylum system by prioritizing asylum seekers who most need asylum in the United States,” Francisco wrote in the brief order. “The rule also screens out asylum claims that are less likely to be meritorious by denying asylum to aliens who refused to seek protection in third countries en route to the southern border.”

Opponents of the policy were blasting the move on Wednesday.

Sotomayor claimed it would upend “longstanding practices regarding refugees who seek shelter from persecution.”

Lee Gelernt, deputy director of the ACLU’s Immigrants’ Rights Project, agreed — saying the rule “would eliminate virtually all asylum at the southern border, even at ports of entry, for everyone except Mexicans.”

“The court should not permit such a tectonic change to US asylum law,” Gelerny wrote in a response to the high court’s brief order. “Allowing the ban to go into effect would not only upend four decades of unbroken practice, it would place countless people, including families and unaccompanied children, at grave risk.”

Most migrants attempting to cross the southern border through Mexico and Central America are fleeing violence and poverty, but the majority of them are ineligible under the new rule, according to experts.

The ACLU believes that the updated policy is “far more extreme” than what was initially proposed by the Trump administration.

“The first one at least allowed individuals who presented themselves at a port of entry to apply for asylum,” Gelerny said. “The current ban would eliminate virtually all asylum at the southern border, even at ports of entry, for everyone except Mexicans.”

With Post wires