A federal judge has temporarily halted President Donald Trump’s White House ballroom project, blocking further demolition of the East Wing and putting the $400 million plan on pause while the legal fight plays out.

NBC reports that U.S. District Judge Richard Leon said the National Trust for Historic Preservation was likely to win its claim that no law gives Trump the authority to bulldoze ahead without Congress signing off.

“The President of the United States is the steward of the White House for future generations of First Families. He is not, however, the owner!” wrote Leon.

The ruling lands in the middle of a fight over how much power a president has to reshape one of the country’s most famous buildings. Leon’s order stops demolition, site prep, excavation, foundation work, and other construction tied to the ballroom.

Leon gave the administration 14 days before the injunction takes effect, so it can appeal; the department filed a notice of appeal about 90 minutes after the decision, signaling the White House is not backing down.

Trump has pushed the ballroom as a privately funded upgrade and has said the project will not cost taxpayers anything. Though preservationists argue the East Wing demolition should not have moved forward without a formal review process. The trust sued in December, saying the administration skipped the checks that normally come with major changes to a historic federal site.

The judge’s line that the president is the White House’s “steward” but “not… the owner” is likely to resonate well beyond this case, especially as the fight over the ballroom becomes another test of how far Trump can stretch executive power.

“Congress is the collective voice of the American people in our system of government,” Leon wrote. “[A]nd the Constitution itself vests authority over federal property, including the White House, in Congress!”