Nearly a dozen activists barged into the Metropolitan Opera on Monday night and brought a performance of Tchaikovsky by Russian artists to a halt in protest of Vladimir Putin’s anti-gay laws.

With celebrity guests including Brooke Shields, Heather Graham and Diane Kruger looking on, the activists shouted slogans such as, “Putin, end your war on Russian gays!”

Others began shouting the names of the show’s star, Anna Netrebko, and artistic director Valery Gergiev, saying, “Your silence is killing Russian gays!”

Heather Graham and other celebs attended Monday’s show.Curtis/Startraksphoto.com

The 6:30 p.m. performance of “Eugene Onegin” by the 19th century Russian composer Pyotr Ilyich Tchaikovsky — long said to have been gay — had been supposed to be a black-tie affair in celebration of the Met’s opening night.

Protesters, however, showed up outside to denounce laws recently passed in Russia and signed by Russian President Putin that make talking positively about gay and lesbians a crime.

The activist group Queer Nation distributed fliers outside the opera hall at Lincoln Center claiming that Gergiev and Netrebko are “longtime supporters of Vladimir Putin” and that the Met “must counter their anti-gay voices with a statement that expressly condemns Russia’s attacks on [gay] people.”

The fliers also repeated the assertion that Tchaikovsky was gay, which has been debated by historians and recently denied by Russian Culture Minister Vladimir Medinsky.

A witness said the trouble erupted as the opera began.

“Eight to 12 protesters” started yelling from the balconies, “Down with Putin,” and, “Free Russian gays!” the witness said.

“No one expected it,” one patron said. “There was screaming and yelling coming from multiple balconies. People started booing . . . They stopped the opera and guards had to rush in.”

The patron said it took 10 minutes to get the protesters out before the opera began again.

An opera insider said Netrebko was upset backstage at intermission because of the outbursts. She recently expressed support for gays on Facebook.

Gergiev, meanwhile, is clearly a pal of Putin. The Russian leader honored him this year as part of the revamped, Soviet-era Working Hero awards.

Despite the protest, police reported no arrests.

A rep for the Met said there were fewer protesters inside the opera. “There were only four protesters located in the Family Circle,” she said. “The disruption occurred before the performance began and lasted less than five minutes.  They were escorted out peacefully.  Anna herself did a live ‘plazacast’ interview, which was seen in Times Square and the plaza [outside Lincoln Center] and she was not upset at all.”