Nine members of the Kennedy family have joined the legal fight to stop President Donald Trump from building a 250-foot triumphal arch near Arlington National Cemetery, filing a motion on Tuesday to intervene in two existing federal lawsuits against the project.

The plaintiffs, children and grandchildren of former Senators Robert F. Kennedy and Edward M. Kennedy, argue the arch would obstruct views of their relatives' gravesites and the Eternal Flame commemorating President John F. Kennedy. They say the granite, gold-ornamented structure would "fundamentally alter the experience of visiting the gravesites" and permanently cast shadows over the hallowed ground, which draws millions of visitors each year.

The filing, brought by veteran Washington lawyer Norm Eisen and the Democracy Defenders Fund, contends that the National Park Service and the Department of the Interior authorized the arch without the required congressional approval. It also argues the monument would destroy the intentionally designed, century-old line of sight between the Lincoln Memorial and Arlington House across the Memorial Bridge.

The Kennedys join a sprawling roster of plaintiffs that already includes the governments of Washington, D.C., Virginia and Arlington County, as well as Vietnam War veterans and preservationists. Last week, District Judge Tanya Chutkan barred the Trump administration from breaking ground on the structure for 14 days while she considers whether to issue a preliminary injunction.

Speaking for the family, Rory and Maxwell Kennedy, children of the late Senator Robert F. Kennedy, said the action is about "protecting sacred spaces that belong to the American people," noting that several members of their family are among the more than 400,000 veterans and family members buried or honored at Arlington.

Health and Human Services Secretary Robert F. Kennedy Jr., a Trump appointee who is estranged from much of his family, did not join the litigation. A White House spokesperson said it was "unfortunate" that some Kennedys had joined the case, adding that the arch is intended to honor the heroes who rest at Arlington. Trump has said he intends to complete the arch before he leaves office in two years.