AIB has set aside a further €300 million to deal with the tracker mortgage scandal - saying "redress may be due" to a group of customers.
The move comes after a preliminary decision - which has yet to be published - by the Financial Services Ombudsman.
It also comes ahead of the bank's release of their 2019 financial results next month.
The move brings the total fund for tracker mortgages at the bank to €570 million.
AIB said in a statement: "AIB Group plc advises that following a preliminary decision issued by the Financial Services and Pensions Ombudsman, the Board understands that redress may be due to a previously identified group of customers who had an option of a prevailing tracker rate.
"The Board recognises that there is a range of possible outcomes and has created a provision of €300 million which will be taken in full year 2019 financial results.
"The Board also recognises it is in the interests of the Group, our customers and our other stakeholders to bring this matter to a resolution and discussions are ongoing with the Central Bank of Ireland with regard to potential appropriate treatment of this group of customers."
Newstalk's Business Editor Vincent Wall explained that almost 6,000 customers who never had a tracker mortgage are impacted.
He said: "[The customers'] contract said that when the timeframe on their existing mortgage ended, they had the option to get a tracker if they wanted it.
"By the time most of those contracts ended, tracker mortgages had been taken off the market completely because they were costing the banks too much and the financial crash had come... but they had the option, and it seems like they weren't informed properly that they had that option."