The US Supreme Court announced Thursday it would hear arguments next month on President Donald Trump’s push to end birthright citizenship — a principle enshrined in the Constitution for over 150 years.

The Trump administration had filed an emergency application asking the justices to lift or limit lower court rulings that paused an executive order he signed on his first day in office.

Under that order, which was due to take effect February 19, children born to parents in the United States illegally or on temporary visas would not automatically become US citizens, radically altering the interpretation of the Constitution’s 14th Amendment.

Offering no commentary on the case, the court said it would hear oral arguments on May 15, while leaving the halts in place.

When asked about the development Thursday, Trump said he was “so happy.”

“I think the case has been so misunderstood — that case, birthright citizenship, is about slavery,” he told reporters in the Oval Office.

The 14th Amendment was one of several amendments enacted in the wake of the Civil War to guarantee rights to formerly enslaved people, and says, in part: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States.”

Trump’s order was premised on the idea that anyone in the United States illegally, or on a visa, was not “subject to the jurisdiction” of the country, and therefore excluded from this category.

The Supreme Court, in a landmark 1898 case, previously rejected such a narrow definition.

District Judge John Coughenour, who heard one of the cases challenging the action in Washington state, described the executive order as “blatantly unconstitutional.”

“I’ve been on the bench for over four decades, I can’t remember another case where the question presented is as clear as this one is,” said Coughenour, who was appointed by a Republican president, Ronald Reagan.

The birthright citizenship issue will be just one at play in the May 15 hearing, as the justices have technically been asked in the case to limit nationwide injunctions against Trump’s policies.

Like the halt on his birthright citizenship order, many of his other actions have been blocked by lower courts as they work their way through the legal system.

The Trump administration argues that lower courts should be limited in applying halts to policy on a national scale, saying they “gravely encroach on the President’s executive power.”

“This situation is intolerable,” the Trump administration wrote in its emergency request, noting that the number of such injunctions have soared under his presidency.

The Supreme Court has a 6-3 conservative majority, though it is unclear if the case will break down along ideological lines.

The issue has become a rallying cry for Trump and his Republican allies, who accuse the judiciary of stymying his agenda against the will of voters.

Democratic opponents however point to the onslaught of actions by the Trump administration in its rampaging first few months.

The Republican-controlled House of Representatives passed a bill last week to limit judges’ power to issue nationwide injunctions, though the text likely has no chance of passing the Senate.