A court case to determine the future of current account charges will get underway this week.
The Office of Fair Trading (OFT) is facing seven banks and a building society in a test case that could lead to customers being able to claim back millions of pounds of unfair fees.
Last year £570 million worth of unauthorised overdraft and bounced cheque fees were returned to 330,000 customers, as the consumer revolt gained pace with millions of people downloading template complaint letters from advice websites.
The OFT estimates current account providers make £3.5 billion a year from unauthorised overdraft fees.
At the centre of the case is whether banks and building societies are using the fees as a fair and clear penalty, or are using them to make a profit.
The British Bankers' Association (BBA) has defended the industry saying "the fees customers pay for unarranged overdrafts are fair and clear", but welcomed the case for providing "legal clarity".
Angela Knight, BBA chief executive, said: "Establishing legal clarity on the issue of bank charges is of paramount importance, not only for the banking industry, but for all customers now and in the future."
During the case all claims for unfair current account charges have been put on hold, but consumers are being urged to continue lodging complaints.
However, a final decision from the court over whether the OFT has the power to act against the banks under Unfair Terms in Consumer Contracts Regulations is not expected until Easter and an appeal is expected to follow.
It is feared if high fees are deemed unfair, banks and building societies could start charging for running bank accounts for all consumers.