Lawyers for the 43,500 ANZ Bank customers who filed a class action lawsuit against the lender, seeking $57 million in damage, said the claims could balloon into multi-billion dollars.

YouTube/nzheraldtv

The legal counsel told the Federal Court in Melbourne on Monday at the start of the three-week hearing at the largest consumer class action in the country's history that the ANZ case is just the first of eight planned class action lawsuits involving 185,300 customers of eight banks who are claiming $243 million in excessive over limit, late payment and other bank fees between $25 and $45 that the claim were illegal and not proportionate to actual cost.

They explained that since public pressure made the National Australia Bank (NAB) reduce its fees in 2009, the banks had illegally collected $5 billion in these fees for at least six year. Once the fees have been established in the court case as penalties, then it would apply to all the banks customers for all of the fees charged on them, said Andrew Watson, class action head of the Maurice Blackburn law firm.

"That is a huge issue that will constitute a precedent not just for the banks that we've used but for other financial institutions who are levying similar fees and exceptions charges," The Australia quoted Mr Watson who believes it has a strong case which could open similar class action lawsuits in other industries.

James Middleweek, investment manager of IMF, which funded the class action lawsuit, added that NAB no longer collection such fees and ANZ cutting these fees drastically to just $6 because of consumer pressure would make it hard for the banks to justify the higher fees they used to collect.

The Federal Court hearing was the result of a High Court decision in 2012, opening the door for the trial of the class action lawsuit.

The other banks that are part of the wider class action suit are Citibank, Commonwealth Bank, NAB, St George, Westpac, BankSA and Bankwest, while the ongoing hearing versus ANZ would be a template for the other actions.