AIB is to give redress and compensation to 5,900 customers following a decision on their tracker mortgage cases.
The bank had previously admitted that it had denied these individuals the chance to go back onto a tracker after they came off a fixed rate, but it argued that the tracker rate was prohibitively high at the time.
AIB said in February it announced that it had made an additional provision, primarily in relation to a Financial Services and Pensions Ombudsman decision on an individual case relating to a tracker complaint which was then at a preliminary stage.
"This case is now concluded with the FSPO. While this case involved a number of complex issues the bank has decided to accept the finding in full, and to apply the finding to other customers within the same cohort," AIB said on its website.
"Customers do not need to take any action and will receive a letter and their payments in July and August," it added.
AIB had offered each of the group just over €1,600 in recognition of a service failure but is now giving them payments which consumer advocate Brendan Burgess calculates could be in excess of €30,000 on a €200,000 mortgage.
Brendan Burgess said that AIB's behaviour has been appalling.
"They have dragged this out for four years instead of facing up to the problem and redressing the customers," he said.
Mr Burgess has called on the Minister for Finance to veto the appointment of the non-executive directors of AIB who appear to have never questioned the strategy of the bank's management.