More than 100 jobs have been put at risk as part of a restructure by Bank of New Zealand, a workers' union says.

First Union, which represents staff at major banks across the country, says the bank is undergoing a "massive" and unnecessary reshape of 30 of its branches.

"It's appalling that a wildly profitable bank like BNZ is looking to put so many people out of work," union spokeswoman Tali Williams said.

She said the changes were hitting frontline tellers, and that Smart ATMs couldn't replace people.

"Sure, Smart ATMs can assist if you want to make a deposit, but what about all the other reasons people visit a bank?" Ms Williams said.

"Smart ATMs cannot approve loans, give financial advice, or help sort out a problem in someone's account."

The union says the bank is proposing to cut jobs and hours at stores across the country and that changes had already occurred in some despite still being in the consultation phase.

Comment has been requested from BNZ.