After the lights dimmed for the Metropolitan Opera’s Russian-themed opening night gala on Monday evening, the first solo voice that rang out in the house was not of a tenor or soprano, but of a protester criticizing the recent antigay laws signed by President Vladimir V. Putin of Russia.

“Putin, end your war on Russian gays!” a man shouted in the vast auditorium, which was packed for the black-tie gala opening of Tchaikovsky’s “Eugene Onegin,” before turning to two of the evening’s Russian stars: Anna Netrebko, the popular Russian diva, and Valery Gergiev, the artistic director of the Mariinsky Theater in St. Petersburg. “Anna, your silence is killing Russian gays! Valery, your silence is killing Russian gays!”

Some members of the audience tried to shush the protester, as security guards walked into the house. After a pause, the opera began.

Four protesters in the Family Circle were asked to leave and did, opera officials said.

At issue was a new law banning “propaganda on nontraditional sexual relationships” that Mr. Putin signed into law in June, drawing worldwide attention to the difficulties gay people face in Russia. Both Ms. Netrebko and Mr. Gergiev were vocal supporters of Mr. Putin in his last election.