NEW YORK (JTA) — As with many exclusive events, the Metropolitan Opera House’s Opening Night Gala on Monday had a few uninvited guests.

But these weren’t your typical party crashers.

Thousands of demonstrators gathered outside the Met chanting “Shame on the Met!” and “Say no to the show!” in protest of the Metropolitan Opera Company’s decision to produce the controversial opera “The Death of Klinghoffer.”

The John Adams opera, which debuted in 1991 and is set to premiere at the Met on Oct. 20, depicts the 1985 hijacking of the Italian cruise ship Achille Lauro by Palestinian terrorists and the murder of Leon Klinghoffer, a 69-year-old Jewish-American passenger in a wheelchair.

Protesters charge that the production is anti-Semitic, hostile to Israel and sympathetic to terrorists. On one line from the production, the hijacker Molqi sings: “We are/soldiers fighting a war/We are not criminals/and we are not vandals/but men of ideals.”

The Anti-Defamation League has said that while the opera itself is not anti-Semitic, “there is a concern the opera could be used in foreign countries as a means to stir up anti-Israel sentiments or as a vehicle to promote anti-Semitism.”

Under heavy criticism, the Met decided in June to cancel a planned global simulcast of the opera. But it stuck to its decision to stage the show in New York.

“It’s one of the most disgusting things ever done by an opera or cultural institution,” one protester, Phil Rosen, said at the demonstration on the Met opera season’s opening night.

Among the protesters were former New York Gov. George Pataki, Rep. Eliot Engel (D-N.Y.), and state Assemblymen David Weprin and Dov Hikind.

Sarri Singer, who survived a 2003 suicide bus bombing in Jerusalem, said the opera “denigrates the humanity of victims of terrorism everywhere.” She likened “The Death of Klinghoffer” to a play about 9/11 — a popular argument among protesters.

“If we give power to allow this production to justify what terrorists do, then what is going to happen next?” Singer said to the crowd. “Do we justify those that flew into the World Trade Center here in New York years ago?”

None of the protesters interviewed by JTA had seen the show, but many said they had seen snippets of the libretto.

“The pro-terrorist bias begins with the title: It should be ‘The Murder of Klinghoffer,’ ” read one sign at the protest.

Peter Gelb, the Met’s general manager, maintains that the opera is a work of “genius.”

“To suppress this work of art, which is what they want, would be the worst possible thing,” Gelb said in an interview broadcast on a large screen outside the Opera House. The Met “would be victimized from the very people themselves who have been victims.”

Some finely dressed attendees of the opera gala were greeted with hostility from the sign-wielding protesters and said they felt unfairly attacked. A woman who identified herself as Susan said she had been called “Cinderella” and heckled with shouts of “Shame on you!”

“It’s awesome in our country everyone can voice their opinion,” she said. “But for someone to come up and insult us directly, that’s crossing a line. That causes people to not listen to what you have to say.”

Multiple Met employees declined to comment on the protest, whose sponsors included the Simon Wiesenthal Center, the Zionist Organization of America, Americans for a Safe Israel, AMCHA, the Catholic League, the Christians’ Israel Public Action Campaign, the One Israel Fund, StandWithUs, Strength to Strength and several New York-area synagogues.