What a circus.

A ritzy Manhattan arts club banned the heiress to the “Ringling Bros” fortune for refusing to put diapers on her service dogs — and now she’s barking mad about it, according to a new lawsuit.

The National Arts Club — an exclusive Gramercy Park institution whose celebrity members have reportedly included Mark Twain, Theodore Roosevelt and Martin Scorsese —  effectively booted heiress-cum-columnist Karen Feld from its historic building, she claims in the suit.

Feld, a longtime journalist whose father owned Ringling Bros. and Barnum & Bailey Circus, had been bringing her two small-breed pooches, Mango and Beignet, to events at the club’s posh Victorian mansion to help with her PTSD and seizure disorders, the suit claims.

But the National Arts Club’s food and beverage director suddenly booted her from a May 19 event that she’d attended with her pups as a guest of a National Arts Club member, according to the suit, filed this week in Manhattan Supreme Court.

Feld said she’d been scheduled to return the following day for a luncheon for the Silurians Press Club — a group of veteran journalists where she serves as a board member.

But the press club’s incoming president then passed along a message from the venue declaring that Feld “would not be permitted to attend that day’s scheduled luncheon with her service dogs… unless the service dogs wore dog diapers,” the suit claims.

The club cited “sanitation concerns” — but Feld contended the pooches “had been professionally groomed.”

Feld, dubbed a “District gossip columnist and socialite” by the Washington Post, said she was left “humiliated in front of colleagues and excluded from an event of an organization on whose board she served.”

She called the diaper excuse a cover for alleged illegal disability discrimination, according to the lawsuit.

Feld “has attended NAC events for approximately twenty years with her service dogs and, prior to the events described herein, had never received any complaint concerning the dogs,” her suit claims.

Federal and state law dictate that service animals must be permitted in any space open to the general public — which would seemingly apply to the National Arts Club as it routinely hosts events open to non-members.

Businesses are also limited in what they can ask about service animals, prohibiting all questions beyond if the animal is required and what task it performs.

According to the federal Americans with Disabilities Act, service animals are not required to have any special equipment, including vest, ID tags, harnesses or, presumably, diapers.

But if a service animal is not housebroken, or otherwise under control, it can be removed.

In a statement denying Feld’s claims, the National Arts Club contended her furry friends twice had accidents inside the posh building.

“In the first incident, the dogs soiled Club property, which was documented,” it said. “In a separate incident, detectable noxious orders consistent with the dogs having urinated were reported in the Club’s private member spaces.”

According to her suit, Feld — whose father, Irvin Feld, was dubbed  “the man who saved the circus” after buying the Ringling Bros in 1967 — usually keeps her pups nestled in a travel carrier bag when attending events.

Feld claims the National Arts Club is also retaliating against her by “threatening” the press group’s ability to continue to hold events at the Gramercy Park building while her litigation is pending, according to court papers. The suit also claims the NAC has launched a pressure campaign to shove her off of her board position with the Silurians.

The National Arts Club said it “denies Ms. Feld’s meritless claims, denies that she has suffered damages as a result of the Club’s actions, and looks forward to defending itself in court.”

“Ms. Feld has previously filed numerous lawsuits involving a variety of matters, including accessibility claims relating to her dogs,” the club’s statement claimed.

Feld sued her estranged brother, Kenneth, in 2011, alleging she was assaulted during a shiva for the beloved aunt who raised the pair.

The siblings first battled when their circus maven dad died in 1984 and Feld discovered she had been cut from the will. Feld reportedly sued her brother for $10 million but later settled for less than $1 million.

Kenneth, who’s net worth is now reportedly $2.5 billion, ultimately took over the family business and renamed it Feld Entertainment.

Feld’s lawyer declined to comment.

–– Additional reporting by Joyce Cohen