About 9,500 Tesco staff are to hold a series of one-day strikes at its 75 supermarkets from June 25th.
A ballot by Mandate and SIPTU found 93 per cent in favour of industrial action over low rates of pay. Mandate has 9,000 members in Tesco and SIPTU has 500.
"The company has consistently failed to take seriously the issue of low pay," Mr John Douglas, Mandate's national industrial officer, said yesterday.
Tesco's director of corporate affairs, Mr Dermot Breen, said the balloting process had been conducted before "established industrial relations procedures" had been exhausted. "The outcome of today's trade union ballot is as we expected. Our staff, however, have not been balloted on the significant pay offer we have made."
The two unions refuse to recommend the Tesco offer to their members on the grounds that it is not enough. No further negotiations are planned before strike action is due to begin.