Justice Michelle Gordon found that ANZ's credit card late fees of up to $35 were a penalty and were "extravagant and unconscionable", especially in comparison to the overall cost to the bank, which could be as little as 50c.
She also waived the usual six-year time limit on legal action.
While some aspects of the decision are being appealed to the Full Court of the Federal Court - by ANZ and the law firm that took class action on behalf of bank customers - Mr Hooker said Fair Play on Fees would be making the same arguments against Westpac and BNZ.
More than 41,600 people had registered to take part in the class action so far, and Mr Hooker urged any other affected customers to sign up before the end of tomorrow's working day.
"Educated estimates" suggested the amount allegedly unlawfully charged to members of the suit was "very roughly an average of $1000 per person", Mr Hooker said.
A spokeswoman from Westpac said the bank would "review the proceedings when we receive them and we continue to encourage customers with concerns to contact us directly".
A BNZ spokeswoman said the bank would review details of any proceedings once papers had been served.
The Fair Play on Fees group is already involved in similar class suits against ANZ and Kiwibank and is working on a case against ASB Bank.