More than 100 jobs are at risk as the BNZ restructures its branch network, the union representing the workers says.
According to First Union, BNZ is proposing job and hours reductions for tellers in more than 30 branches nationwide and more cuts are happening "every day".
The union has slammed the restructure as unnecessary and called it "appalling" that such a profitable bank was looking to put so many people out of work.
"BNZ's restructure impacts frontline tellers, the first people to help us when we walk into a branch," said First Union spokeswoman Tali Williams.
"This isn't just devastating for those staff who may lose their jobs but it'll impact customers as well. When jobs go customer service suffers."
Williams said the bank claimed "smart ATMs" were making people obsolete, but this did not take into account all the other reasons people visited a bank.
"Smart ATMs cannot approve loans, give financial advice, or help sort out a problem in someone's accounts. Many customers still want face-to-face service. You only need to go into any branch to see there are lines out the door so there's still a customer need," she said.
"This is an uncertain time for BNZ workers and their families and bank workers across the country are asking 'who's next.'"
A statement from BNZ said that in some of bank's branches it was looking at "the mix of staff and skills they have".
"For some this means there are change proposals that are being discussed. We can't go into detail on what that might be as we need to let the proper consultation process take place with our people in the first instance," the statement said.
"In the past, we've spoken about the need to get the balance right as our customers become increasingly independent when it comes to their day-to-day banking. Most are comfortable using things like online banking and our app, and smart ATMs which can process more transactions and queries."