Preservationists are pressing ahead with their lawsuit against President Donald Trump's planned $400 million White House ballroom, declining a request by the Department of Justice to withdraw the complaint following the shooting at the White House Correspondents' dinner on Saturday.

Trump and other conservatives have made a renewed push for the ballroom in the wake of Saturday's media dinner shooting, arguing it exposed the difficulties in ensuring presidential security at large events outside the White House grounds, and urging the National Trust for Historic Preservation to drop its lawsuit.

Top Justice officials said the government would ask a court to dismiss the lawsuit "in light of last night's extraordinary events" if the Trust did not voluntarily drop it.

Trust attorney Gregory Craig declined that request, writing to the Justice Department that the legal issues at the heart of the lawsuit are unchanged.

"What Saturday's awful event does not change is that the Constitution and multiple federal statutes require Congress to authorize construction of a ballroom on White House grounds, and that Congress has not done so," Craig wrote.

A spokesperson for the Justice Department did not immediately return a message seeking comment.

The preservation group sued in December, a week after the White House finished demolishing the East Wing to make way for a ballroom that Trump said would fit 999 people. Trump says the project is funded by private donations, although public money is paying for a below-ground bunker and security upgrades.

In its lawsuit, the Trust argued that Trump had overstepped his authority by moving forward with the project without first getting approval from key federal agencies and Congress.

A federal appeals court has allowed Trump to continue the project, ruling a day after a lower court judge continued to block above-ground construction on the site and scheduling a June 5 hearing to review the case.