Choristers at the English National Opera are to be balloted for industrial action in a dispute over jobs and pay.
Members of Equity will vote in the coming weeks on whether to launch a campaign of action.
The union said the 44 singers were facing a 25% pay cut and the loss of four jobs.
Equity warned the cuts could push the world renowned ENO into "terminal decline ".
The choristers attended a news conference in London, and sang a Pirates Of Penzance song to demonstrate their quality.
Equity said it feared bigger pay cuts if the proposals go ahead.
As well as the pay cuts and job losses, managers were also planning to increase hours, remove payment for Sunday working and stop overtime pay, said Equity.
The ballot will be for strikes and other forms of industrial action and Equity said it was ruling nothing out.
Productions could be halted by any action.
Stephen Spence, assistant general secretary of Equity, warned against "cultural vandalism" in trying to balance the books.
"We are attempting to retain the artistic integrity of the ENO.
"This is a flagship national opera company, which always sings in English, nurtures home grown opera singers and is world renowned. "
Equity official Hilary Hadley said ENO initially wanted to make savings of £500,000 but the figure had increased to £900,000, raising fears of bigger pay cuts.
The choristers are paid £32,900, and would find it difficult to continue living in London if they lost a quarter of their salary, said Equity.
The Arts Council of England wanted a progress report on the proposed cuts by the end of next month, according to the union.
The choristers were not allowed to give their names because of contractual arrangements, but they said they felt let down by the proposals.
One told the Press Association : "I am angry and upset. We are one of the hardest working departments and in many ways we are the heart and soul of the company.
"Some people are already looking for another job."
The choristers went on strike in 2003 in a row over jobs, which halted one production.
Cressida Pollock, chief executive of the ENO, said: "We have some difficult decisions to make over coming weeks as we seek to find ways to remodel our business so that we can weather a £5 million cut from our core Arts Council grant.
"ENO is a solvent company and will remain that way. To place the company at threat of another financial crisis would be to risk the future of one of the UK's greatest cultural assets.
"In short, we need to find a way to bridge the gap that a £5 million annual shortfall in funding leaves. That will mean producing different work, performing in different spaces, raising more money and increasing our box office revenues.
"It also, inevitably, means finding ways to save costs whilst preserving our artistic quality.
"We have reviewed our overhead expenditure and our administration staff and our administrative teams have been cut by 30% over the past 10 years. We are a lean operation.
"It is not our intention to further casualise the workforce at ENO. We remain committed to retaining a permanent chorus, orchestra and backstage team."