Bank of Ireland is investigating a problem with laser card transactions conducted since last Friday, which resulted in double charging in some cases.
The bank is set to refund millions of euro to the affected customers.
Bank of Ireland has confirmed that 120,000 of its customers were affected by the problem which emerged in the last few days.
It is understood that laser card users who used their cards since last Friday have been double charged for the same purchase - possibly repeatedly over a number of days. However, the bank has yet to clarify whether the problem also affected transactions in the days since Friday.
The banks said that the payment of direct debits and cheques were not affected by the glitch, while a small number of Standing Order payments may have been delayed by one day.
A spokeswoman for Bank of Ireland this morning said all refunds had been made, including all overdraft fees and penalties charged to customers who were put into the red as a result of the incorrect charges to their card.
However, the bank said it was not yet in a position to identify how the problem occurred, or at what point it was identified.
In a statement this morning, it apologised to customers for this error. It said that customers who are concerned in relation to this error should contact Banking 365 on 1890 365 365 or contact their local branch.
