More than 2,000 Marks and Spencer workers are to go on strike tomorrow.
Despite the mass walkout coinciding with one of the busiest shopping days in the run-up to Christmas, trade union Mandate insisted workers do not want to strike during the festive season.
Assistant general secretary Gerry Light said management had forced their hands in a row over the closure of a pension scheme.
"Management have not given sufficient evidence that these cost-saving proposals are justified," Mr Light said.
"And in that context it is difficult for the workers to accept the unilateral imposition of cost-saving measures, like the closing of the defined benefit pension scheme which, unlike many, is performing and has a current surplus of 17 million euro (£14.3 million)."
Staff voted overwhelmingly in favour of a wave of festive walk-outs last month in the deepening row with bosses.
Mandate, which says it represents the vast majority of the 2,300 employees in the retail chain's 17 shops across the Irish Republic, has argued that workers have no choice but to strike.
It said the company had proposed a string of other cuts, including a reduction in the Sunday and public holiday premium paid to staff, the scrapping of the Christmas bonus, and a reduction in the number of section managers.
Tomorrow's walkout will be the first of a number, with two further days of action planned before Christmas.
Pickets will also be staged at the stores after 94% of those balloted backed a protest.
Mr Light also claimed that the company's repeated statements about wanting to meet to resolve the dispute are disingenuous.
"Notwithstanding the pre-emptive attack on our members' terms and conditions, the union attended two conciliation conferences at the Labour Relations Commission in order to find a resolution," he said.
"However, despite being requested to defer some of the implementation dates for the removal of our members' much-valued entitlements to facilitate meaningful engagement, management refused to agree."
He urged Marks and Spencer to return to the negotiating table with a "genuine determination" to agree a settlement that is acceptable to workers.
"Our members do not want to take industrial action and are genuinely hurt and disappointed with the way their employer has treated them," Mr Light added.
"We're urging the company to act in a manner which is befitting of the perception that the public has of Marks and Spencer as a reputable employer and give their workers the respect and a resolution to this dispute that they undoubtedly deserve."
Later, a Marks and Spencer spokesman accused unions of misleading employees and customers to gain support for this "disruptive strike".
"We will not be put off course by the threat of industrial action," he said.
"The impact of diverting now would be hugely detrimental to our customers, our employees and our business and put our plans for future investment in doubt.
"We hope that the unions will come to realise this and agree to reopen meaningful negotiations to prevent any further disruption and inconvenience for our customers and employees."
The spokesman said the organisation was willing to restart talks as soon as possible to discuss additional business reforms and compensation in lieu of the closure of the defined benefit pension scheme.
Marks and Spencer said contrary to claims from union representatives that the majority of employees are affected by the pension scheme closure, only a third will in fact be affected.
It added that claims that the scheme has a surplus of more than 17 million euro (£14.2 million) were also inaccurate.
It said an independent review carried out by Deloitte confirmed as of March this year that the scheme was showing a deficit of 12.6 million euro (£10.5 million).
The 17.5 million euro (£14.6 million) figure, it claimed, is based on a minimum funding standard which is unrealistic for a scheme with so few retired members.
Trade union Siptu confirmed its members who work for Marks and Spencer will take part in the strike.
It said the 140 workers would also take part in the further two days of action - on December 12 and 20.