ANZ's retail managing director, Kerri Thompson, said the bank would "vigorously defend" the claim.
Mr Hooker, who is backed by Australian law firm Slater & Gordon, urged any ANZ customers looking to join the suit to sign up because once the court documents were filed at the High Court next Tuesday it would be difficult to include others.
He said if every ANZ customer joined the suit, overcharged exception fees could total about $250 million.
More than 25,000 have joined the campaign so far and Mr Hooker said law suits against the country's other major banks, including Kiwibank, were imminent.
Overdrawn accounts, bouncing cheque and late credit card payments usually incur fees of $10 to $20, but Mr Hooker claimed the real cost to banks is a few cents.
The lead plaintiff for the ANZ case is Aucklander Sandra Cooper, whose cleaning business banked with National Bank before last year's merger.
Ms Cooper, in her 50s, said she'd been hit with about $1500 in default fees, making her "a typical claimant".
Many of her charges were forced overdraft and dishonour fees.
In December 2009, a direct debit pushed her account into $27.55 overdraft for three days and she was charged a $10 fee. Slater & Gordon class-action lawyer Ben Hardwick claimed the bank effectively charged her an interest rate of 4400 per cent.
The other two lead plaintiffs are Mr de Menefy and Craig Jones, a beneficiary from Papatoetoe, who believes he's owed $1000 - mostly for unarranged overdraft fees.
Mr Hooker said the case was all about the difference between the fees charged by the bank, and the cost to it of managing the default.
"If these fees were fair, the banks would have justified the need to charge their fees by now. Their silence says it all."
Ms Thompson said the claim had come as a surprise to ANZ.
"It's a sad day when US-style litigation arrives in New Zealand," she said.
Ms Thompson said the bank was upfront about its exception fees, which were set out in the terms and conditions provided to its customers.
"Exception fees are avoidable and the vast majority of New Zealanders don't pay them in any given year," she said.
"We are not aware of large numbers of customers being unhappy with the exception fees outlined in our terms and conditions."
She described the action as unnecessary, unfortunate and one which risked subjecting customers to a long and expensive legal process with no guaranteed outcome.
Taking action
Who can register?
Anyone who believes they have been overcharged exception fees.
Register at www.fairplayonfees.co.nz
What fees are included in the class action?
* Honour fees when there are insufficient funds in an account to meet a direct debit payment or cheque. The bank pays the money but then charges a fee.
* Dishonour fees where a person is charged for going into overdraft which has not been arranged.
* Late payment fees on a credit card.
How much does it cost?
Legal services are being provided on a "no win, no fee" basis so there is no upfront fee but the company funding the action, Litigation Lending Service, will take 25 per cent of any payout.
How long will it take?
It could be two to three years.
