Over 400 customers at a branch of Dunnes Stores in Ennis, Co Clare, have had unauthorised deductions made from their bank accounts.
The error occurred when purchases were paid for with a Laser debit card, it emerged today.
One customer who contacted ireland.comsaid he was charged for the price of his purchases multiplied by a factor of ten.
He said when he complained he was told by a Dunnes Store representative that 409 similar errors had occurred.
The company confirmed a number of laser card and credit card transactions between Tuesday November 13th and Monday November 19th had been replicated a number of times.
"This error only affected the Ennis store and while all errors have been rectified by Dunnes Stores, due to delays in the banks’ clearing systems, a number of these errors may not be corrected in customers’ accounts until Monday next, November 26th," a company statement said.
The company who supplied the software to Dunnes, IBM, said the error has now been rectified.
"We were informed immediately by Dunnes Stores and IBM technical and management staff met with the company to identify the technical problem and this has now been resolved," Mr Rory Caren, IBM's communications manager, said.
Dunnes Stores said it sincerely regretted the errors had occurred and apologised to customers who were affected.
"We have written to a number of customers to express our apologies and we invite any customers who may have any concerns to contact the store manager at Dunnes Stores, Ennis," the company statement said.