A group supporting 6,000 AIB customers, who were denied a tracker mortgage despite a contractual right to one, has urged those affected to lodge an appeal before the deadline next week.
A year ago the bank acknowledged that it should have offered the customers concerned trackers at the prevailing rate when their fixed rates expired.
However, it argued that if they had been placed onto the prevailing tracker rate at that time, they would have been at a disadvantage, as it would have been higher than the standard variable rate.
The customers were offered €1,615 by way of settlement, for the failure to offer an option they were technically entitled to under contract.
But a group calling itself the AIB Tracker Campaign Committee has urged those impacted to lodge an appeal with the Independent Appeals Panel in the bank before the deadline expires next Friday, 15 March.
According to the committee, a group of the customers is planning to try to force the bank to provide redress to all 6,000 of those affected by taking a case to the High Court.
However, if a customer has not lodged an appeal with the panel, they will lose their right to take any further action, the committee advises.
In a statement, the bank said it is now in the final stages of its tracker mortgage investigation.
"The customer grouping in question did not hold a tracker mortgage," it said.
"Notwithstanding this fact, AIB has provided them with a payment.
"We are in the final stages of the Tracker Mortgage Examination with payments issued to the vast majority of customers. Over 99% of impacted customers have received payment.
"The review is ongoing and is subject to continuous engagement with the Central Bank."
AIB stopped offering trackers to new customers in 2008 and has argued that those coming off fixed rate home loans after that could not have been placed on the prevailing rate because there was not one.
But the committee believes the borrowers should have been placed onto a rate of the ECB rate plus 1.25%, as this was the last rate offered to customers who left a fixed rate and remained in place until the end of 2013.
If appeals are successful, the customers could be entitled to substantial refunds of overcharged interest, dependent on the date their fixed rate ended and the size of the mortgage.
The group estimates that this could be worth as much as 15% of the initial mortgage amount in each case.
Committee co-ordinator Brendan Burgess called on new AIB CEO Colin Hunt to make resolving this issue a priority so that the High Court action will be unnecessary.