The US Supreme Court on Wednesday is hearing arguments on the legality of President Donald Trump’s directive to restrict birthright citizenship in America, an executive order which declared that children born to parents who are in the US illegally or temporarily are not American citizens.

Trump, who is attending the Supreme Court arguments, sought to undo the birthright citizenship with an executive order on his first day in office and override the US Constitution, or according to Trump administration’s arguments, interpret the constitution in a correct manner.

The Supreme Court justices are expected to hear the arguments in Trump administration’s appeal against a lower court’s verdict from New Hampshire that had struck down citizenship restrictions. Trump’s executive order haven’t taken effect anywhere in the US, AP reported.

The lower court ordered that Trump’s policy violated citizenship language in the US Constitution’s 14th Amendment and a federal law which codifies birthright citizenship rights. Trump will become the first sitting president of US to attend Supreme Court’s oral arguments.

The Supreme Court is expected to rule in the matter by the end of June. Reversing the birthright citizenship is part of Republican administration’s broad immigration crackdown. And it is the first immigration related policy of Trump administration which has reached the court for a final ruling.

In a Truth Social post against the court, Trump on Sunday said, “Birthright Citizenship is not about rich people from China, and the rest of the World, who want their children, and hundreds of thousands more, FOR PAY, to ridiculously become citizens of the United States of America. It is about the BABIES OF SLAVES! Dumb Judges and Justices will not a great Country make!”

If the Trump administration secures victory in the court, it would completely change the view that the Constitution’s 14th Amendment, ratified in 1868, and federal law since 1940 gives citizenship on everyone born on American soil.