Mandate, the Irish shopworkers' union, is threatening legal action against Dunnes Stores if it refuses to back down in a dispute over Christmas bonuses.

The company has traditionally paid its 10,000 staff a bonus of one and a half weeks' pay for Christmas working, but three years ago it replaced the cash payments with vouchers for the company's stores.

Some staff objected and demanded the cash equivalent, but Dunnes refused. The staff claim was upheld by an independent industrial relations arbiter, but Dunnes challenged his decision, arguing that vouchers were benefits in kind and outside wages legislation. However, an employment appeals tribunal has now ruled that the vouchers should be considered under pay laws.

Its chairman, Peter O'Leary, said that he was of the opinion that as the vouchers could be bought for cash at any of Dunnes' outlet, it followed that they were therefore "interchangeable with cash".