A Manhattan restaurateur says the leaders of an Upper West Side synagogue are acting like “La Kosher Nostra” — threatening to destroy his business if he doesn’t allow their $1.8 million legal dispute to be heard in religious court.

Joseph Allaham — whose kosher restaurants draw celebrities like Madonna and Ricky Martin — says officials from the Lincoln Square Synagogue promised to yank the kosher certification from his eateries if he didn’t comply with their demand to go before their preferred Jewish arbitrator, according to court papers.

Losing his kosher seal would be a death blow to Allaham’s food empire — which includes the kosher steakhouse Prime Grill on Madison Avenue, the Upper East Side rooftop eatery at the Bentley, and the Yorkville gourmet-food store Prime Butcher Baker — since many of his customers are religious Jews.

Allaham has been fighting with the modern Orthodox synagogue — where US Supreme Court Justice Elena Kagan had her bat mitzvah — over a catering deal that went bad. The restaurateur claims in a new Manhattan civil suit that he agreed to help the Lincoln Square Synagogue build a new banquet hall as part of their new $50 million complex on Amsterdam Avenue and provide the catering for it.

But the construction was delayed. Allaham says that cost him business, and the synagogue says he owes them $300,000 in unpaid fees for use of the hall and $1.5 million for his share of building it.

But last month, synagogue officials sent Allaham a notice requiring him to take the dispute out of the civil court and in stead have it heard before the Beth Din of America, a rabbinical court.

Allaham is resisting because he says Rabbi Shaul Robinson of Lincoln Square is a member of the organization that oversees the tribunal. “That’s the conflict of interest,” Allaham told The Post.

He also tried to downplay the dispute with the synagogue — which counts composer Steve Reich and former “Late Show” sidekick Paul Shaffer as members.

“We’re not fighting,” Allaham insisted, adding that he wasn’t “threatened,” by religious leaders, rather he was “asked to comply.”

However, in papers filed Thursday in Manhattan Supreme Court seeking a stay of the religious arbitration, he said they threatened to pull his kosher license if he didn’t go to the Beth Din.