Ulster Bank has been fined €37.7m by the Central Bank over its role in the tracker mortgage scandal.
It is the largest fine ever given by the Central Bank.
Nearly 6,000 Ulster Bank customers wrongly lost good-value tracker mortgages.
Widespread overcharging meant 43 of those customers lost properties, including 29 family homes.
The Central Bank also criticised the way Ulster Bank dealt with the scandal as customers began to complain.
It said that, at this time, the bank assessed the potential cost to the business and decided to only provide the correct rate to people who complained.
Those who did not complain were not restored to the correct rate until the Central Bank intervened.
Central Bank Director of Enforcement Seana Cunningham said: “Despite it being clear to [Ulster Bank] from customer complaints that certain customers were paying more for their mortgage than they should be, [it] continued to deny customers the lower tracker rates that they were entitled to.
She added that the bank “only did right by its customers following intervention by the Central Bank.”
After 2015, when a Central Bank review of the tracker issues was ongoing, banks were told to ensure customers did not suffer “further detriment” pending the finalisation of the review.
However, failures in Ulster Bank's internal procedures meant some customers were not told they may have been impacted by the scandal.
Seven of the 43 lost properties were lost because of these particular failings.
The scandal started during the last financial crisis. A number of customers who moved on to fixed rates were not returned to their tracker rate when the fixed period was over, even though they were entitled to get their good-value tracker back.