The National Trust for Historic Preservation said Monday that it will not drop its lawsuit to halt construction of President Donald Trump's White House ballroom, despite the Justice Department's request.

"We are not planning to voluntarily dismiss our lawsuit, which endangers no one and which respectfully asks the Administration to follow the law," said a statement from Carol Quillen, the head of the trust.

The trust's statement comes one day after the Justice Department wrote a letter urging the group to drop the suit, arguing that the "lawsuit puts the lives of the President, his family, and his staff at grave risk."

Karoline Leavitt, the White House press secretary, spoke about the ballroom project in her press briefing on Monday, making the case that it needs to be completed.

"The White House ballroom project is not just a fun project for President Trump like you will read in the media," Leavitt said. "It is actually critical for our national security that a larger, secure building on this complex — which is the most secure complex in the world — is built to accommodate not only large amounts of guests, but also the president, the vice president, members of the Cabinet."

"The line of succession in this country should be able to gather freely and safely without the fear of threats or political violence and the White House ballroom will provide that," she continued. "And so it's critical that we get this project done as quickly as possible."

The Justice Department did not immediately respond to a request for comment.

The shooting at the White House Correspondents' Association dinner on Saturday raised fresh questions about securing events with a slew of high-profile guests, including the president, vice president, Cabinet officials and members of Congress — several of whom sat in the presidential line of succession.

In the hours after the suspect was apprehended, Trump and his allies argued that the ballroom was necessary to provide a more secure setting — even though it's far from certain that the event would be held on White House grounds. The dinner is hosted by members of the media, not the government.

In her response to the Justice Department's letter, Quillen expressed gratitude for Secret Service and law enforcement's response to the shooting and noted that ballroom construction is currently allowed to continue until June 5, the date of the next scheduled oral arguments.

"We have always acknowledged the utility of a larger meeting space at the White House. Building it lawfully requires the approval of Congress, which the Administration could seek at any time," she said in the statement.

Brett A. Shumate, the assistant attorney general for the Justice Department's civil division, said in his letter to the trust's lawyer that Saturday's incident proved the ballroom "is essential for the safety and security" of the president and others.

"When the White House ballroom is complete, President Trump and his successors will no longer need to venture beyond the safety of the White House perimeter to attend large gatherings at the Washington Hilton ballroom," Shumate said.

Presidents frequently travel around the country and the world for events. Trump himself has attended numerous other large gatherings, including sporting events, conferences, dinners and rallies.