STATE-rescued AIB has been inundated with complaints from angry customers after they were sent letters telling them they owe the bank an average of €30 in charges for three months' banking.
Some 900,000 of the bank's customers became exposed to maintenance fees and transactions charges on their current accounts after new rules.
Letters have been going out all week to customers itemising the charges incurred between May and August.
The money will be taken out of accounts in the next two weeks.
From May 28, anyone who keeps less than €2,500 in their current account is being charged a maintenance fee of €4.50 every three months, and between 20c and 30c per transaction.
It is understood that thousands of customers unable to keep a credit balance of €2,500 in their accounts have complained bitterly to the bank about the new charging structure.
Before last May, customers were able to qualify for free banking by staying in credit, making just one purchase on their debit card and carrying out one transaction through phone or online during the quarter.
Chief executive of the Consumers' Association lobby group Dermott Jewell last night accused the bank of being mercenary by imposing such tough conditions on consumers.
He said most customers would find it impossible to keep a credit balance of at least €2,500 every minute of every day each quarter.
"AIB has mirrored Bank of Ireland and made it incredibly difficult to escape charges," he said.
Bank of Ireland charges 28c per transaction and a quarterly fee of €11.90 for those who do not meet its criteria.
Customers must keep a balance of at least €3,000, or lodge at least €3,000 and make multiple transactions online to avoid the fees.
AIB, which is 99.8pc owned by the State following a €21bn bailout, is closing 67 branches across the country.
Last night, AIB defended the regime, saying the change was driven by the need to recover costs across the bank.
It said it was expensive to provide current accounts. "An aggressive cost-reduction plan is in place at AIB with the aim of returning the bank to viability," a spokeswoman said.
The bank has about 1.5 million current accounts.
The over-60s, students and those with graduate accounts will continue to have fee-free banking.
But more than 900,000 customers are likely to be hit with charges.
About 200,000 AIB customers who had Cashsave accounts have been exposed to charges for the first time after the bank closed off these accounts.
Half of the 400,000 who have a Cashsave account used it for day-to-day banking as the account came with a Laser card.
These people would have direct debits and standing orders as part of the account.