Equity said its members backed strike action by 93% on a turnout of 100%, and called for talks to avoid walkouts.
The union said WNO chorus members are facing at least a 15% cut to their pay, a reduction in contracted hours despite their high workload of performances and rehearsals, and a fall in the number of chorus members.
Compulsory redundancies are a “real threat” in a group that is already under-resourced, said Equity.
General secretary Paul W Fleming said: “This ballot result is a resounding vote of no confidence in Welsh National Opera management and shows that chorus members will not take their disastrous cuts.
“Our members are tired of being told to be resilient, and just get by. This is a resounding vote for resistance to management’s willing acceptance of the political choice of austerity.
“WNO must go back to the drawing board on these unjust proposals and engage in a process which protects the full-time status of our members and recognises the huge value this highly skilled workforce bring to the reputation of the company and to its work.”
Equity workplace representative Claire Hampton, a soprano who has been in the WNO chorus for 22 years, said: “My colleagues and I voted in favour of taking strike action and action short of strike, reflecting our dismay at proposals to cut our salaries and contract length. This was not an easy decision for any of us to take, but we have been left with no choice as we face the devastating impact that proposed changes will have on our income.
“If management are unwilling to negotiate an improved offer, we are committed to taking action to protect our jobs. This disruption can be avoided by meeting our simple and achievable demands for a full-time contract, fair treatment, adequate resources and respect for the work that we do.”
A WNO spokesperson said: “While we respect the decision of the ballot organised by Equity who represent WNO chorus members, we are disappointed that this will mean our audiences will ultimately miss out due to the effect on performances/concerts.
“We have continued to engage in open and transparent negotiations with unions and are committed to finding a solution which works for our chorus members while also recognising the reality of WNO’s financial situation following significant cuts to our public funding.
“It wouldn’t be appropriate for us to comment further at this time.”
