A U.S. federal appeals court on Friday ordered President Donald Trump's administration to stop construction on a $400 million ballroom on the site of the White House's demolished East Wing, dealing the Republican leader a major setback in a case testing his presidential authority.

The Washington-based U.S. Court of Appeals for the District of Columbia Circuit in a divided 2-1 order upheld a preliminary injunction won by the National Trust for Historic Preservation, which sued last year after the administration tore down the East Wing and began building a 90,000-square-foot (8,360-square-meter) ballroom without seeking authorization from Congress.

The appeals court placed its ruling on hold for 14 days to allow the Trump administration to appeal to the U.S. Supreme Court.

Trump appealed after U.S. District Judge Richard Leon twice blocked above-ground construction on the site while allowing underground work to continue.

Leon, an appointee of Republican former President George W. Bush, had ruled that no federal statute "comes close to giving the President" the required authority to construct the ballroom without congressional approval.

The ballroom plan, which the administration has described as necessary for large formal functions and to preserve the safety of the White House, is the grandest of several Trump efforts to reshape central Washington's landscape of government buildings and national monuments.

A judge in a separate lawsuit recently said Trump's name was illegally added to the exterior of the Kennedy Center performing arts center and ordered its removal.

In the ballroom case, Justice Department attorney Yaakov Roth said during D.C. Circuit arguments on June 5 that the courts have no role in weighing the privately funded project and that it would have been improper to block it at any point.

Roth said the National Trust's "architectural preference" against the ballroom shouldn't take precedence over national security concerns, claiming evidence that the former East Wing left the president and others in the White House vulnerable to attack.

"They just don't want to go to Congress," countered Thaddeus Heuer, a lawyer for the preservation group.

Trump has defended his ballroom and its price tag, which has doubled from initial projections. Trump said in a post on Truth Social last month that the cost rose because "it is approximately twice the size, and a far higher quality, than the original proposal" and promised "it will be magnificent, safe, and secure!"