The Australian and New Zealand Banking Group (ANZ) is set to face a $50 million class-action lawsuit filed by an estimated 27,000 ANZ account holders in the Melbourne Federal Court on Wednesday.

Lawyer Bernard Murphy, chairman of Maurice Blackburn law firm, said that the legal action called into attention on ANZ's illegal practice of ripping off thousands of its clients in the past six years, stressing that "we allege that the exception fees that are being charged are simply illegal because they are a penalty."

Mr Murphy added that ANZ employed contracts on transaction that were completely unfair and unconscionable.

He said that a case in point was Mark Murphy's construction business which maintained an account with ANZ and ended up with bank fees that totalled to $35,000 for the past six years, all from a single account and incurred through numerous daily transactions that were crucial for the operation of his Sydney-based company.

Mr Murphy now joined thousands of ANZ customers, who all cried foul over the unrealistic banks fees imposed on them, in filing the lawsuit that largely trains its focus on exception fees, dishonour fees, over-limit fees and late payment fees on credit cards.

In its initial reaction, ANZ chief executive Philip Chronican said that the bank would have to defend itself against the accusations as he conceded that the fees were indeed unpopular with customers.

Mr Chronican said in light of their clients' reactions on the fees, ANZ has endeavoured to simply the fees since December 2009 and meet the bank customers' expectations as he asserted that "it's a big leap, however, for a fee to go from being unpopular to being unlawful."

Consumer advocates Choice and The Australian Institute threw their support behind the class-action suit and urged more ANZ customers to join the legal actions, which according to Maurice Blackburn could recover up to $1,500 in bank fees should the case becomes successful.