The US Supreme Court has dealt a blow to President Donald Trump’s agenda to end birthright citizenship for children of illegal migrants.

In a 6-3 ruling, the divided court upheld a 150-year conception of birthright citizenship.

Trump’s executive order had declared that children born to people who were in the US illegally or temporarily were not citizens.

It’s the second major legal blow to one of Trump’s initiatives following the court striking down his global tariffs.

The justices relied on the 14th amendment, adopted after the Civil War, and recent federal laws in ruling that anyone born in the US, with very limited exceptions, is a citizen.

Trump issued the order last year on his first day back in office as part of a suite of policies to curb illegal ‌immigration.

Reacting to the decision on social media, Trump posted that it was “too bad for our country”.

But he said he would pursue his agenda instead through legislation in Congress.

“No long and unwieldy Constitutional Amendment is necessary! Congress should start TODAY to work on ending expensive and unfair to our Country, Birthright Citizenship.

“They will have my Complete and Total Support!”

The justices upheld a lower court’s decision that blocked Trump’s executive order directing US agencies not to recognise the citizenship of children born in the United States if neither parent is a US citizen or legal permanent resident, also called a “green card” holder.

Challengers to Trump’s order argued that ‌it violates language in the US constitution’s 14th amendment that confers citizenship to those born in the United States who are “subject to the jurisdiction thereof”.

During arguments in April, both conservative and progressive justices questioned the administration order’s legality in a momentous case that was magnified by Trump’s unprecedented attendance in the courtroom.

Trump’s order would have upended widely held views that the 14th amendment confers citizenship on everyone born in the United States, excluding only the children of foreign diplomats and those born to a foreign occupying force.

During the arguments, US Solicitor General D John Sauer, representing the administration, said the promise of citizenship for virtually any baby born on US soil has spawned what he called a sprawling industry of “birth tourism”.

Sauer said that “uncounted thousands of foreigners from potentially hostile nations have flocked to give birth in the United ​States in recent decades” ‌to secure citizenship for their children.

Asked to explain how serious an issue “birth tourism” has become, Sauer primarily cited media reports and conceded that “no one knows for sure.”

The 14th amendment was ratified in 1868 in the aftermath of the Civil War of 1861 to 1865 that ended slavery in the United States, and overturned a notorious 1857 ​Supreme Court decision that had declared that people of African descent could never be US citizens.

During arguments, Sauer described what he saw as the limited purpose of the 14th amendment Citizenship Clause, saying it was adopted “to grant citizenship to the newly freed slaves and their children, whose allegiance to the United States had been established by generations of domicile here.”

The ​legal challenge to Trump’s directive considered by the Supreme Court, which has a 6-3 conservative majority, involved a class-action lawsuit filed in New Hampshire by parents and children whose citizenship was threatened by the directive.

The Supreme Court weighed in on what it means to be an US citizen just ahead of ‌the July 4 holiday when the United States ‌marks the 250th anniversary of its founding.

Trump urged Congress on ‌Tuesday to end ‌birthright citizenship after the Supreme Court’s decision.

“The Supreme Court upheld Birthright ⁠Citizenship, ‌which is too ​bad for ​our Country, ‌but we can ​easily make it up ​in Congress ​through ​Legislation,” Trump ‌wrote in a post on Truth Social.

-with AP