The Kennedys have sued to stop construction of President Donald Trump’s “triumphal” arch.

On Tuesday, nine members of the dynastic political family filed a motion in federal court in Washington, D.C., to block the arch from being built, arguing that it would obstruct views of the family’s gravesites at Arlington National Cemetery, including that of President John F. Kennedy.

“This action is about protecting sacred spaces that belong to the American people,” Rory Kennedy and Maxwell Kennedy, two of the plaintiffs and children of the late Sen. Robert F. Kennedy, said in a statement on Tuesday. “A towering arch casting shadows across the graves of our father, mother, and uncles, as well as the graves of so many who have served our country, would also cast a shadow over our democratic principles, undermining the safeguards established by our elected representatives to protect this hallowed ground for generations to come.”

The plaintiffs include the children and grandchildren of the late Sens. Robert F. Kennedy and Edward M. Kennedy, who are among several Kennedy family members buried at Arlington National Cemetery, the U.S.’s largest military cemetery. Other Kennedys buried or memorialized there include JFK, first lady Jacqueline Kennedy Onassis, their two children Patrick and Arabella, as well as Robert F. Kennedy’s wife Ethel, and Lt. Joseph P. Kennedy Jr.

Health and Human Services Secretary Robert F. Kennedy Jr. is not among the plaintiffs.

The family argued that the 250-foot arch—“more than double the size of the Lincoln Memorial and the equivalent of a twenty-five-story office building”—would obscure views of the John F. Kennedy Eternal Flame and Kennedy gravesites from the Arlington Memorial Bridge. It also argued that it would “cast shows over … the memorials of hundreds of thousands of fallen American heroes.”

The arch’s proposed site is located in Memorial Circle between the Lincoln Memorial and Arlington National Cemetery, which the family argue would obstruct “a line of sight that was designed to represent the unification of the Nation following the Civil War and that has existed for nearly a century.”

“The gigantic proposed arch is an illegal interference with Arlington National Cemetery and the heroes remembered there,” attorneys Norman Eisen and Steve Jonas of Democracy Defenders Fund, which represents the family members, said. “Only Congress has the constitutional power to authorize an intrusion of this magnitude.”

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The Kennedy family is not the first group to mount a legal challenge against the project. Their Nov. 10 filing seeks to join a lawsuit filed last month by D.C. and Virginia, which argued that the arch violates historic preservation laws and would hinder traffic and emergency services. It also argued that the project did not have congressional authorization. That lawsuit was consolidated with an earlier suit filed in February by a group of three veterans and an architectural historian. It is being overseen by U.S. District Judge Tanya Chutkan, an Obama appointee.

The Kennedys argued that courts have previously recognized families’ interests in protecting their relatives’ burial sites.

Arlington County also filed a separate lawsuit in October, alleging that the government had failed to adequately review the project’s environmental impact, including its consequences for traffic and public safety.

The arch has faced significant backlash from Democratic lawmakers, preservationists, and the public. During a nine-hour-long public hearing on Thursday, dozens of people testified against construction of the arch. Preservationists pointed to an August review by the National Park Service in which the Administration noted the arch would have an “adverse” impact on up to 42 historic sites.

But the hearing ultimately ended in the National Capital Planning Commission approving the project, and the National Park Service and Interior Department authorized construction of the arch late Thursday.

Chutkan then blocked any “construction-related activity” for 14 days.

The arch is one of several of Trump’s projects to remake the capital, many of which face legal challenges. Trump has begun building a $400 million, 90,000 sq ft White House ballroom, resurfaced the Lincoln Memorial Reflecting Pool, sought to renovate the Kennedy Center with his name on the building, and proposed redeveloping the historic East Potomac Golf Links. Trump has invoked national security to justify the arch and the White House ballroom, announcing in September that he would incorporate a military complex into the proposed arch to house drones, snipers, and ammunition.

The President has said he wants to see the arch erected before he leaves office, although the mounting legal challenges threaten that timeline. In his first public appearance after Republicans’ sweeping losses in the midterm elections, Trump repeated his defense of his attention to the construction projects: “For me, it’s relaxing.”