A new report has warned that Union Station's standing as a D.C. architectural icon would be in jeopardy if a modernization by Amtrak moves forward as planned.

"Amtrak's conceptual plan, as it was presented to the public, remains vague on how exactly the proposed changes would impact the physical structure or visual appeal of the historic station," DC Preservation League Executive Director Rebecca Miller said last week.

Miller's comments came with the release of a report compiled by the league and other preservationist groups that says Amtrak's modernization plan to expand railroad facilities and other planned developments could damage the landmark's historic value if they fail to respect its unique place in the city.

"Several stakeholders want to make dramatic changes that could improve the station -- or undermine an architectural and community icon," the report, titled, "A Golden Opportunity to Re-invest in Historic Union Station" stated.

An Amtrak spokeswoman defended the company's plan and said it looks forward to meeting with community groups as it moves forward with is modernization project.

"Amtrak's Washington Union Station Master Plan matches the quality and vision of the original, iconic Union Station design, while creating a world-class transportation hub and preserving Union Station as an architectural treasure," Christina Leeds said in an email, adding that the company "welcomes the input of the preservation coalition and has begun to coordinate a dialog with them."

The report cites other planned projects that affect the station's future, including interior rebuilding and refurbishing for retail, expanded transit facilities like the H Street Trolley and a major planned development over the station's railroad and metro tracks to the north.

Because of the likelihood of substantial taxpayer investment in some projects, any plans concerning Union Station's future must involve meaningful public engagement, said Stephanie Meeks, president of the National Trust for Historic Preservation, which also helped produce the report.

The release also recommends that a preservation plan guiding the construction be created for the station before these major projects kick off. In addition, authors believe that the public "must" participate in the station's master planning and that any additional development should "embody" Union Station's historic Beaux-Arts design.

Real estate firm Akridge is building a 3 million-square-foot development of residential, office, retail and hotel complex built on a platform over the station's railroad tracks. That project, an undertaking nearly as massive as the Pentagon, is still in the early planning stages.