One of Australia's largest banks faces a multimillion dollar payout to thousands of customers after a judge ruled that late payment fees it charged on credit cards were exorbitant.

ANZ Banking Group Ltd. partially lost a class action law suit in the Australian Federal Court on Wednesday brought by more than 43,000 customers who claimed they had been charged excessive fees for years.

Justice Michelle Gordon ruled that the bank had been illegally imposing penalties for late payments on credit cards.

But she also ruled in ANZ's favor by dismissing claims that other types of bank fees were illegal penalties.

Lawyers for the bank and customers have until next week to agree on a proposal for repaying customers for the court to rule on.