Tesco employees in the Republic of Ireland are set to go on an indefinite strike from 26 May.
The strike was to initially begin from Monday but had been postponed due to talks between Tesco and Workplace Relations Commision (WRC).
However, now with the breakdown of the negotiations, the employees of 70 stores have again decided to launch an indefinite strike.
The stores collectively employ around 5,000 people.
This dispute began when the firm planned to shift around 300 of its employees hired before 1996 to new contractual terms, which were claimed to be less favourable than for those who were appointed at a later date.
Mandate trade union general secretary John Douglas was quoted by RTE News as saying: "It will mean between 15% and 20% reduction in their earnings for those workers. It'll mean that they have to make themselves available any time between 7am till 11pm, five days over seven, so Monday to Sunday, to work.
"It'll mean that they'll lose any guaranteed overtime that they may have accumulated over the years. It'll mean that they have to be totally available at the beck-and-call of the company to come in any time they want them to."
The workers union said that the strike will be called off if Tesco takes the case to Labour Court.
Douglas told Irishtimes.com: "This is not a company under pressure or on the verge of closure. They won't go to the Labour Court because they know their cause is unjustifiable. The WRC asked them and the company said they needed 24h to make up their time that ended at 3am this morning."
The supermarket firm employs around 14,000 people in 140 outlets across Ireland.