Allied Irish Bank has confirmed that it is writing to approximately 11,500 customers over discrepancies with insurance options on credit cards.
AIB said it started a review of credit card accounts last year after customer feedback.
The discrepancies found relate to insurance options on credit cards, including payment protection plan, travel insurance and card protection.
The customers inadvertently paid these charges and will receive refunds totalling €3.1m.
AIB has said that the Central Bank has been notified and it apologises to the affected customers.
It says letters will be issued to them and they will be refunded in the coming days.
It said: "The review programme was conducted in line with established and agreed customer refund processes.
"Where documentation was reviewed and any doubt existed in relation to the validity of the Bank's customer information the benefit was applied to the customer."
