If you thought that the fight to save the Plaza Hotel is over, I’m afraid you are only half-right. Yes, those famous white exterior walls will remain as is, but if certain people have their way, the most important part of the Plaza could go the way of Penn Station. On June 28, the Landmarks Preservation Committee will take up the issue of deciding whether the interior of the Plaza, including the Palm Court, will remain the beautiful and elegant link to another era or be turned into the entrance to a shopping mall.

Imagine turning the apses in St. Patrick’s Cathedral into retail shops (its location at 51st Street and Fifth Avenue is certainly prime) or gutting the interior of Radio City Music Hall in a similar fashion. There are certain spaces that just define New York and the Plaza is certainly at the top of the list. Although the earlier fight to save the Plaza resulted in a compromise to keep at least part of it as a hotel, the larger fight has still not been resolved: saving its unique interior spaces – an important piece of our great city’s history and grandeur – from gross mutilation.

In order to have an interior space designated as a landmark, it must meet three criteria: It must be more than 30 years old, it must be a place to which the public is customarily invited, and it has to have special historical or aesthetic interest or value as part of the heritage and culture of the city. There are few interior spaces in New York that fit these criteria better than the Plaza. The Palm Court, the Grand Ballroom, and the Edwardian Room have been the public spaces where New Yorkers have convened to hear our country’s presidents and the world’s statesmen. It is where we have presented our daughters, supported charities, and watched our children get married. Beyond that, it is also part of our national heritage – celebrated in our literature by F. Scott Fitzgerald in “The Great Gatsby.” For children throughout the world, it is where Eloise romped and played. It’s where Cary Grant sauntered through the lobby so elegantly and where he was kidnapped in Alfred Hitchcock’s “North by Northwest.”(Grant didn’t have to rehearse the scene because he walked through that lobby every time he was in New York – he maintained an apartment in the Plaza.)

Recently, the Plaza was acquired with the intention of converting the guest suites into apartments, which would accommodate and thrill only the very rich and detach the portion of the building overlooking fabulous Central Park so it is no longer accessible to the public. The compromise that was reached with the help of the city and the Hotel Workers Union would allow one-third of the building to be dedicated to a “new” hotel. But it could hardly be called a grand hotel. Now this new Plaza hotel could close its landmark restaurants so they would no longer serve the public as they have for almost a century. And here’s the worst part of the plan: The hotel lobby would be converted into a common entry for a massive shopping mall to be sunk in the building’s basements combined with the wonderful meeting space known as the Terrace Room. Instead of an idyllic retreat – one of the last reminders of another era – the Palm Court would be used as a huge pedestrian traffic entryway and corridor to an enormous shopping center, thereby guaranteeing that the new hotel would become a concept more suited to a suburban shopping mall rather than a magnificent hotel overlooking Fifth Avenue.

This developer acquired the property well knowing that a retail shopping mall could not be constructed because of zoning laws. But through a quirk in the city’s preservation laws, “underused rentable space” in the hotel’s basements, in combination with the Terrace Room, could be disemboweled and sold for use as a retail mall after the developer closed the Plaza and dismembered the property by separating the 58th Street and 59th Street sides of the building.

This is hardly a hardship case. The developer reportedly spent $675 million for the acquisition of the property with the intention of cutting up the building into three pieces and selling them separately. The Landmarks Preservation Conservancy has urged the “owner/developer to agree to maintain the historic appearance and use of its rooms as a fundamental part of preserving the Plaza Hotel.” But it is unclear this will actually happen.

Ultimately, what gives the Plaza its historic and cultural significance is not its exterior – which is magnificent – but its interior. It’s not the walls of the Plaza … it’s what you do with the space between those walls. It’s the public space and our usage of that public space over the last century that makes the Plaza important to us all.

Forty-four years ago, New York sadly made perhaps its most horrific architectural mistake when it allowed real estate developers to destroy the old Pennsylvania Station. In its place, tens of millions of commuters have had to suffer with an airless, crowded hole in the ground instead of the grand, open, magnificent space that was the old station. In an admission of that fatal error, the Post Office project is an attempt to bring back part of what once was – but at a cost of billions of dollars. Wouldn’t it be sad if our grandchildren had to wage a similar and costly battle to rebuild a Plaza they would know only through books and photographs?

Mr. Lauder is a businessman and an adviser to the New York Landmarks Conservancy.