An appeals court ordered the Trump administration to halt construction on its White House ballroom, saying the project needs approval from Congress in order to continue.

“Whether or not a massive ballroom should be constructed is for Congress to decide and is not a matter for Executive self-help,” the U.S. Court of Appeals for the D.C. Circuit wrote in a 136-page ruling issued Friday.

The three-judge panel issued a 2-1 ruling, but it says it will stay its order for two weeks to allow the Trump administration to appeal to the Supreme Court.

NPR has reached out to the White House for comment but did not hear back in time for publication.

Within two hours, President Trump slammed the decision, writing on Truth Social that his administration will be immediately appealing the decision, which he called “horrendous, politically motivated and unlawful.” He pointed out that the two judges who sided against him in the ruling were appointed by Democratic presidents: Barack Obama and Joe Biden.

Trump also repeated his administration’s argument that the ballroom is a matter of national security, and that Friday’s ruling threatens it.

The decision “severely jeopardizes the lives and welfare of the people who work, and will be working, at the White House — including all future Presidents of the United States, and their families, as well as the lives of all those visiting, such as Heads of State and other Dignitaries, and all Americans who wish to visit the historic, beautiful Executive Mansion,” Trump wrote.

The nonprofit National Trust for Historic Preservation, chartered by Congress, which brought the lawsuit late last year, celebrated the ruling.

“This is a great day for our country and for the American people’s right to voice their opinions about the historic places they cherish, including the White House,” Brent Leggs, its president and CEO, said in a statement shared with NPR.

Friday’s ruling is the latest chapter in a saga that began in October, when the Trump administration started demolishing the East Wing of the White House to make way for Trump’s long-held dream of a presidential ballroom.

The administration has said the ballroom will total roughly 90,000 square feet and seat 1,000 guests. The White House originally estimated the cost at $200 million, but the Washington Post reported in June — citing contractors’ invoices — that the total cost could be at least $600 million.