The major banks will this week begin their High Court challenge over new rules on the way complaints about controversial payment protection insurance must be handled.
The British Bankers' Association is launching a judicial review against the Financial Services Authority and the Financial Ombudsman Service over new regulations that came into force in December.
The rules aim to ensure consumers are treated fairly, both when they buy payment protection insurance (PPI) and when they complain about being mis-sold the cover.
To ensure people understand what they are buying, providers will have to talk potential customers through the key features of a policy, rather than just provide them with a document giving the information, as was previously the case.
They will also have to provide evidence to show that it was made clear to the customer that the cover was optional if it was taken out alongside credit.
But the banks are unhappy that the rules will apply to complaints relating to PPI policies which were sold before the new regime was brought in.
The BBA said: "We believe the FSA is effectively creating a precedent which permits it to apply new rules to previous sales - even where those sales were regulated by other FSA rules."
It said the policy was like having a road with a speed limit of 30mph, which was later changed to 20mph, and deciding to hand out speeding tickets to people who drove at 30mph before the limit was reduced.
PPI covers debt repayments if the holder is unable to work due to an accident or illness or if they lose their job, but it has come in for heavy criticism after research found it had been mis-sold to many consumers who would never be able to claim on it while others felt pressurised into taking it out alongside a loan or credit card.
The cover is currently the single most complained about product to the Financial Ombudsman Service, with the group receiving nearly 2,600 complaints during the past week alone. It is also finding in favour of consumers in 86% of PPI cases, suggesting the banks are not handling the complaints properly.