The US Court of Appeals for the DC Circuit, which had allowed construction to continue while it considered the case, agreed with a lower court that such a massive White House overhaul required the explicit consent of Congress.
It stayed its own decision for two weeks to give Trump time to ask the Supreme Court to intervene.
The Republican president lashed out after the 2-1 ruling, calling it “horrendous, politically motivated, and unlawful.”
The two judges in the majority were appointed by Democratic presidents, while the dissenter was nominated by Trump himself.
The president vowed in a lengthy social media post to immediately appeal to the Supreme Court.
“This decision, made after much of the work has been done and paid for, is a National Security Threat at the highest level. It is also a National Disgrace,” Trump said in another post on his Truth Social platform Friday night.
Trump initially touted the construction of the ballroom as being necessary to host galas, but has since repeatedly pointed to the concurrent addition of an underground military bunker and other security features.
Under the district judge’s initial order, work was to be allowed to continue only on a limited set of structures, including those that were underground.
“This holding has nothing at all to do with whether the proposed ballroom is desirable, or not, as a matter of policy. This ruling does not even necessarily mean that the Defendants may not ultimately construct the ballroom,” the majority wrote Friday.
“What it does mean is that the Defendants may not do so during the district court’s expeditious litigation without securing Congress’s authorization, as the Constitution and laws require.”
Trump, who has repeatedly complained that the White House lacks sufficient space for grand galas such as state dinners, unilaterally ordered construction of the massive ballroom.
Work on the project began last year with the sudden demolition of the White House’s entire historic East Wing.
Since then, photos have shown significant work on a basement complex, with some concrete walls rising up above ground.
Trump has insisted that the ballroom will be privately financed, but media reports in June showed that significant taxpayer funds were going to the project, which could cost as much as $600 million.
While the White House initially cited a $200 million price tag for the project, it quickly doubled the estimate to $400 million.
The ballroom is just one of Trump’s pet projects to leave his mark on Washington by the time he leaves office in 2029, along with a renovation of the Lincoln Memorial Reflecting Pool and other parks, as well as the construction of a gigantic arch.
Several of the projects have similarly faced legal challenges, but the ballroom project would be the first to reach the Supreme Court.
