Tesco staff in Sligo and Carrick-on-Shannon are striking this weekend in a row over pay and conditions.
Workers in Sligo are walking off the job for the third time this month.
In the Carrick-on-Shannon store, staff plan to strike tomorrow for the first time.
Mandate Trade Union claims Tesco has not engaged with them in an effort to resolve the dispute.
John Douglas, Mandate General Secretary, said: “It is unfortunate that our members are forced to strike yet again due to Tesco’s continued refusal to engage with their workers’ union and follow collective grievance procedures.
“Our members don’t want to be on strike, but it seems the company is happy to prolong this totally unnecessary strike for their own reasons.
"We hope the public will understand the necessity for our members to defend their interests and put the blame firmly where it belongs, with Tesco management.”
Tesco released a statement saying they are extremely disappointed with the strike action.
They said: "This series of one-day strikes is entirely out of proportion as these are local disputes involving local issues that don’t warrant such disruption in Christmas week. Despite the strikes, our stores will remain open today and Saturday and we thank our colleagues and our customers for their co-operation.
"We regret this action by Mandate and the disruption inflicted on our colleagues, our customers and to other businesses in the two towns by these unjustified strikes. It is particularly disappointing action by Mandate for these close-to-the-Border towns in the run-up to Christmas.
"We reject Mandate’s claims that the union is left with no option but to have strikes in Sligo and Carrick-on-Shannon or that it is Tesco’s failure to follow and implement agreed collective procedures. It is in fact the complete opposite, we remain committed to the State’s industrial relations machinery as we were before when we accepted a Labour Court recommendation that continues to remain rejected by Mandate. Unlike the union, we continue to respect the Industrial Relations processes and remain committed to them.
"Tesco remains committed to resolving this dispute. We request that Mandate, even at this late stage, desist from the industrial action and refer these issues back to the WRC where we are willing to engage with the union. Mandate should return to the agreed norms in industrial relations as is provided for in our current agreement and call off this unnecessary and damaging action.
"Mandate should revisit too its decision to refuse to take up the offer from the WRC for a conciliation conference on Sligo which was originally scheduled for October 24th. In Carrick-on-Shannon the local issues have not yet even been referred back to the WRC by Mandate indicating these strikes are pre-emptive.
"It is unfathomable that Mandate is taking this approach when Tesco fully respects our colleagues’ right to choose to be represented by a trade union, unlike many other retail stores and businesses this Christmas who do not recognise or engage with Mandate. "