The 60 singers have refused to appear in tonight's scheduled performance of Berlioz's The Trojans - The Capture of Troy, at the London Coliseum.
In protest at the planned job cuts, they will instead stage a free recital of Verdi's Requiem at St Paul's Church, in nearby Covent Garden.
Equity, the performers' union, said that the singers had voted unanimously in favour of industrial action after ENO threatened to reduce their number by one third as part of a cost-cutting programme.
Equity added that ENO management had so far not responded to requests to discuss alternative methods of achieving savings.
A further four one-day strikes are planned, on April 3, April 16, May 8 and May 25. ENO is due to embark on a formal 90-day consultation with staff about redundancy packages and selection process next week.
ENO has been plunged into financial crisis in recent years, and says a grant offered by the arts council is dependent on the company revising some of its practices.
A spokeswoman for the organisation said that the changes could only be achieved through "a combination of reduced staffing levels, more flexible ways of working and new contractual relationships".
Although she was unable to confirm whether 20 chorus jobs would be cut, she stressed that "a policy of no change is not an option".
Last week, the ENO chairman, Martin Smith, described the strike action as "deeply disappointing".
