The US Supreme Court in a 5-4 ruling on Monday let Donald Trump’s administration continue construction of his White House ballroom complex while the US president challenges a judicial order that would halt much of the development, with Chief Justice John Roberts in a dissent calling the project “likely unlawful”.

The court granted the administration’s request to block a lower court’s order halting above-ground construction of the US$400 million ballroom while a lawsuit by a historic preservation group seeking to stop the project proceeds.

Trump hailed the ruling on Monday, saying it removed all further threats to the project which would now be completed by mid-2028.

“I am pleased to report that the United States Supreme Court has just ruled in favor of the Ballroom/Military Complex being built without any further contingency, doubt, or threat,” Trump wrote on his Truth Social network.

The National Trust for Historic Preservation sued last year after the administration tore down the ‌White House East Wing and began building a ballroom without seeking specific approval from Congress. Trump has said the ballroom will be “the greatest of its kind ever built”.

Monday’s ruling was powered by five of the court’s six conservative justices. They wrote that the plaintiffs in the case, the charity National Trust for Historic Preservation, lacked the necessary legal standing to sue. They also said the government would be likely to suffer “irreparable harm” if the project were blocked, citing national security concerns.