A historic preservation group has filed a lawsuit seeking to stop President Donald Trump’s ongoing renovation of the Lincoln Memorial reflecting pool on the National Mall. The Cultural Landscape Foundation, led by founder Charles Birnbaum, says the project violates federal historic preservation requirements and related environmental rules. In the complaint filed Monday, the group argues that the reflecting pool’s original design—including its dark grey, stone-like appearance—has historic significance and that the renovation process is altering that character without proper legal authorization.

The lawsuit contends that the work breaches the National Historic Preservation Act, a federal law that sets procedures for changes to properties with historic value. Reporting also highlights the group’s focus on the replacement or coating of the pool’s surface, including allegations that a blue paint treatment is being applied in a way that is inconsistent with the site’s established historic design.

The filing is part of a broader pattern of legal challenges aimed at Trump’s efforts to remake aspects of prominent Washington, D.C., landmarks. The sources do not indicate a court ruling yet.