WASHINGTON, United States (AFP) –— The United States (US) Supreme Court on Tuesday rejected President Donald Trump’s bid to restrict birthright citizenship, in a blow to one of his signature anti-immigration initiatives.

The court, in an eagerly awaited decision on the final day of its term, ruled 6-3 to maintain the right to American citizenship for nearly everyone born on US soil.

Trump signed an executive order last year on the first day of his second stint in the White House decreeing that children born to parents in the United States illegally or on temporary visas would not automatically become US citizens.

Lower courts blocked the move by the Republican president, ruling that under the Citizenship Clause of the 14th Amendment to the US Constitution nearly everyone born on US soil is an American citizen.

The Supreme Court agreed in a majority opinion penned by Chief Justice John Roberts that was joined by two other conservative justices and the three liberals on the top court.

“Children born in the United States to parents unlawfully or temporarily present are ‘subject to the jurisdiction’ of the United States and are citizens at birth under the Fourteenth Amendment’s Citizenship Clause,” Roberts wrote.

In an unprecedented move for a sitting US president, Trump personally attended oral arguments on birthright citizenship at the Supreme Court in April.

Trump stayed for the presentation by his solicitor general, John Sauer, but did not remain for the arguments of American Civil Liberties Union attorney Cecillia Wang, who defended birthright citizenship.

Wang welcomed Tuesday’s ruling, saying the court’s decision “reaffirms a fundamental American promise — if you are born here, you are a citizen.”

“A president cannot change the constitution by executive fiat,” she said.

Trump called the decision upholding birthright citizenship “bad for our country”.

He urged the Republican-controlled Congress in a Truth Social post to “start TODAY to work on ending expensive and unfair to our country, birthright citizenship.”

“They will have my complete and total support!” he said.

Trump’s bid to end birthright citizenship was part of his wider campaign to limit immigration, which includes expelling millions of undocumented migrants and removing deportation protections from nationals of more than a dozen countries.

During oral arguments before the Supreme Court, Sauer argued that unrestricted birthright citizenship encourages illegal immigration and “birth tourism”, in which foreigners come to the United States solely to give birth.

The 14th Amendment states that, “All persons born or naturalised in the United States, and subject to the jurisdiction thereof, are citizens of the United States.”