Thousands of ANZ customers are part of a class action hoping to convince the High Court the fees are not legal.

It is one of several class actions against the big banks, with the other cases waiting on the outcome of the High Court appeal.

The cases include the Commonwealth Bank, Westpac, National Australia Bank, Citibank, St George, BankSA, and BankWest.

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Initially, the Federal Court ruled in favour of the customers finding the late payment fees were extravagant, exorbitant and unconscionable, and therefore not lawful.

Then Federal Court Justice Michelle Gordon found the late payment credit card fees of up to $35 bore no relationship to the cost to the bank, which was about 50 cents.

Justice Gordon now sits in the High Court and will not be able to take part in the hearing.

Her original judgment was later overturned by a full bench of the Federal Court, prompting the High Court action.

The case has narrowed since it began after both Justice Gordon and the full bench found other bank charges, including over-limit credit card fees, were fair.

One of the lawyers representing the customers, Andrew Watson, said if they won the case it would have ramifications across the banking sector.

“The case will determine principles which affect not just the customers of ANZ but every banking customer in Australia who’s ever paid a late payment fee on a credit card,” he said outside the High Court.

“They (ANZ) could have, if they wanted, charged late payment fees of up to $7,000 per transaction because that was the maximum conceivable cost that could have occurred if someone was one day late paying their credit card transaction.

“We think that’s an absurdity, we’re going to say that to the High Court. We hope we succeed.”