Nineteen rural Westpac branches - from Kamo to Ranfurly - could be set to close, putting 72 jobs at risk, according to the bank workers' union.
Westpac refused to confirm the numbers but said a proposal was before staff. More people were using online banking services, it said.
First Union finance organiser Tali Williams said Westpac should expect community resistance to the closures.
Ms Williams said the bank should be ashamed to be cutting services when it made nearly $1 billion in profit last year.
"I think there's an element of shame that's in the equation for them," she said. "They know they can afford to keep these branches open, and that this is a choice."
The proposal included branches in Kamo, Ranfurly, Carterton, Putaruru and Raglan, she said.
"Westpac will definitely see community resistance to the proposal for closure for the very reason that these communities still need face-to-face service," she said. "Online transactions are just not going to cut it for farmers making major financial decisions, or the elderly who may not necessarily have those resources at their disposal or understand them.
"They also know these communities will be very profoundly affected by these closures - not just the staff but the community itself," she said.
"What we know from our members is that [rural branches] are busier than ever. If anything they feel understaffed. The lines are out the door, they're very busy, so they don't really understand where this [proposal] is coming from."
A Westpac spokesperson said in a statement:
"Customers, as they are around the world, are changing the way they bank and we are continually reviewing how to best meet their evolving needs.
"Currently, more than 85 percent of service transactions with us take place outside of a branch. In addition, over the last five years, online transactions increased by 61 percent and in the last year online logins via a mobile device have increased by 33 percent. This has seen us add 20 Smart ATMs that provide 24/7 service over the last two years, complete nine refurbishments with another five planned before the end of the year in addition to a new site in Auckland.
"A proposal regarding a number of branches is currently with staff for their consideration and feedback. Once that feedback has been received and evaluated a decision will be made.
"Staff and customers will be the first to know that decision and there will be no further public comment until then."
Council keen to keep bank in Ranfurly
Central Otago Mayor Tony Lepper said he would offer the bank space in a council building in Ranfurly, so it could continue to serve the community.
Ranfurly is at the centre of a farming community, and is also on the busy Central Otago Rail Trail, and Mr Lepper told Checkpoint the council wanted to keep the branch open.
"If there's anything we can [do to] help, please talk to us. And I've been back to my chief executive and said 'can we help these people, can we help our community with the service', and she said 'of course, it would be easy, we can work with them'.
"So I need to get hold of Westpac now, and say 'when you are going through these thoughts, keep us in mind', because we'd like to help our community."
Mr Lepper said the closest branch was 90km away in Alexandra, and many people still could not bank online.
In Waikato, Raglan Ward Councillor Clint Baddeley said his community was also heavily reliant on its branch - especially in the busy summer months.
If it closed, residents would potentially have to drive 45 minutes to Hamilton to do their banking if they were unable to do what they needed online, he said.