A High Court test case which could bring a fundamental change to UK High Street banking has been delayed.
The Office of Fair Trading (OFT) is challenging banks and the Nationwide building society on bank charges.
The outcome may decide how much banks can charge millions of account holders who go overdrawn without permission.
The case had been set to begin on Wednesday but the judge's commitments mean it has been postponed. There are hopes it will get under way this week.
The regulator claims that the banks' overdraft charges are unfair, but the banks say they are entirely legal.
"We have always believed that what we are doing is correct and legal," said a spokeswoman for the British Bankers' Association (BBA).
"We are confident and think the hearing is an important opportunity to bring some clarity to the legal position," she added.
The case is an attempt to resolve the legal issues at the heart of the unprecedented wave of mass litigation, which has swept the country during the past two years.