Kiwibank is defending a new phone charge it says prevents people from calling its customer service line incessantly and unneccessarily.
Earlier this year the bank began charging people $5 per call if they rang the line more than five times a month.
Consumer New Zealand said the charge was not in the spirit of the government-owned bank and targeted its most vulnerable customers, such as the poor and the elderly.
"There was a feeling that the big Australian banks were more corporate, cared less, and had higher fees, and Kiwibank would be something different and a bank that Kiwis would feel happy banking with," Consumer chief executive Sue Chetwin said.
"When you see something like this, you have to wonder what their ethos is now."
Kiwibank spokesman Bruce Thompson said the new charge, which was introduced earlier this year, had already proven successful.
"We brought in the fee because we do get overloaded at times and it can be very frustrating for customers," he said.
"We've had a dramatic reduction in the number of calls we've had."
Kiwibank notified its customers who were repeatedly calling its customer service line in advance of introducing the charge, he said.