Bank of Ireland says an extra 6,000 customers are to be included in its tracker mortgage compensation scheme.
The bank says it has set out a "clear path" for the resolution of the tracker mortgage issue for impacted customers.
It says "substantial progress" has been made over the past two weeks.
It says it is now working to ensure that compensation payments are made as swiftly as possible to all affected customers.
Some 4,300 customers will shortly be written to by the bank with an offer of compensation.
It says these letters will also set out a range of options available to customers.
It says it aims to compensate all of these customers by the end of this year.
Group chief executive of Bank of Ireland, Francesca McDonagh, said: "This now gives us a clear picture of the number of impacted customers. The compensation process is commencing, and our priority is to ensure that all impacted customers are compensated as quickly as possible.
"I believe that the way in which we address this issue will define the customer centric culture we aspire to at Bank of Ireland and this is why I have made resolving this issue my personal priority since joining the bank.
"I unreservedly apologise to all impacted customers for the financial loss and anxiety this has caused them and their families."
Thousands of customers of several Irish lenders were overcharged or wrongly denied a tracker rate.
Any Bank of Ireland customer who wants to make contact with the bank on this issue can call the Bank of Ireland Tracker Mortgage Examination Team on 1890-882-722, e-mail firstname.lastname@example.org, or write to: Bank of Ireland Tracker Mortgage Examination, PO Box 400, Castleisland, Co Kerry.