Any Australian bank customer who has ever been charged a late credit card fee is about to be included in what could be one of the country's biggest class actions.

Legal firm Maurice Blackburn has lodged court action on behalf of countless customers of ANZ, Citibank and Westpac to claim back hundreds of millions of dollars in fees.

Action against NAB, the Commonwealth and American Express is expected to follow.

Customers who have been slapped with a late fee do not have to register for the class action, and there is no limit on how far back in time the fees could be recovered.

Gerard Brody from the Consumer Action Law Centre told AM potentially hundreds of thousands of people will benefit.

"It's really unclear at this stage. It's what is known as an open class action so anybody who has been charged this fee could be eligible to benefit," he said.

"That could be many hundreds of thousands of Australians."

Mr Brody says it is unclear exactly how much banks have profited from late fees.

"Some years ago, the banks did change their practices to reduce the fees and we are still seeing the banks' profits [increase], so it hasn't made a huge difference to their bottom line."

Maurice Blackburn lawyer Andrew Watson says, if successful, any customer who has paid a late fee will have a right to compensation.

"We'll be alleging as we have in our earlier case against the ANZ that the late payment fees are penalties and excessive, and customers should get the difference between what they were charged and the true cost to the bank," he said .

Many of the banks are still charging these fees with credit card late payment fees varying amongst the banks.

National Australia Bank charges just $5, while Commonwealth Bank of Australia charges $20.

In February, the Federal Court found ANZ's late credit card fees to be a penalty ruling they were extravagant and unconscionable as they did not reflect the real cost to the bank.

But that ruling is the subject of an appeal.

Banks face strong case

"I think the banks have got a challenge on their hands," Mr Brody said.

"The earlier Federal Court decision this year suggested that the credit card late payment fee was capable of being an unlawful penalty.

"It found the actual cost to the bank was 35 cents, which is much smaller than the many $10, $20 and $50 fees being charged by the banks.

"It is difficult to say with litigation. There's lots of uncertainties, but given the earlier federal court decision, I'd say the case that the consumers are taking is a good one."

At this stage the Australian Bankers Association are not commenting.

ANZ Bank is also not commenting and calls to Westpac and Citibank have not been returned.