Westpac NZ will pay $3.7 million in compensation to 19,365 customers after admitting it breached the Credit Contracts and Consumer Finance Act 2003.
The bank breached the law by failing to provide key information to credit card customers before they entered into their contracts.
Those affected were new credit card customers who received their card without receiving a welcome letter containing disclosure information between May 2017 and March 2018.
Westpac reported the issue to the Commerce Commission in March 2018, who filed High Court proceedings against the bank in July last year.
Gina Dellabarca, Westpac NZ general manager of consumer banking and wealth, said the error occurred during an upgrade to Westpac's IT systems, which resulted in the letter not being sent to more than 19,000 customers.