The union representing singers and dancers at Lyric Opera of Chicago is threatening to strike.

The American Guild of Musical Artists represents nearly everyone on stage at the Lyric: the singers, the dancers, the actors and the production staff. The union is telling its members to be prepared to picket the annual free concert next month and possibly strike on opening night.

Union Executive Director Alan Gordon said the Lyric threatened to lock out workers on Aug. 22 over contract negotiations.

“We’ve made sacrifice after sacrifice in an effort to help Lyric improve its fiscal position, and we do not expect to be paid back by threats,” Gordon said. He said negotiations are stuck because the Lyric wants to cut pay and benefits.

A Lyric spokeswoman confirmed the company is in contract negotiations, but wouldn’t comment because she said it’s company policy not to negotiate in the media.

The Lyric orchestra threatened a strike on the opening night of an opera two years ago over similar issues, saying members couldn’t agree to a pay freeze and shorter seasons that would essentially cut pay. The parties resolved that dispute and avoided a strike.