A Nelson medicinal cannabis seller says the nature of her trade is the likely reason Kiwibank has dropped her as a client.
Rose Renton said the bank had given her 14 days' notice it was closing her account.
It has prompted a Massey Business School director to say a law change was needed to make banks declare why they closed customer accounts.
Renton, a long-time cannabis campaigner was last year named one of Kiwibank's 14 Nelson regional Local Heroes for her work supporting the vulnerable and unwell with cannabis medicines.
Renton had earlier been discharged without conviction on a charge of cultivating cannabis after a judge found her offending was 'altruistic'.
She has been a Kiwibank customer for many years, and while the bank would not say why it had made the decision, she had a fair idea.
"I would say the income I receive from helping the vulnerable in the community is not taxed - although there was a tax account in my banking, and it held the tax from all my earnings.
"There's nothing I hide - all the deposits go straight into that account, so I'd say it's to do with the legality, or illegality of cannabis as medicine."
Renton said up until recently she had $95,000 invested with the bank, and $32,000 sitting in a tax account.
Dr Claire Matthews of Massey University said a bank closing someone's account without reason did happen, but it was not common.
She said banks were not legally obliged to say why, but they should be.
"I would argue it's something that needs to be changed in the related legislation, because there's no (opportunity to) appeal - it's a commercial decision so you can't even go to the banking ombudsman and say: 'They closed my account' unless you've got some evidence as to why they've done it.
"They can just do it and the customer has no recourse."
Kiwibank said in a letter to Renton it had decided it was "no longer prepared" to offer her banking services.
It said it reserved the right under section seven of its general terms and conditions to close the account without giving a reason.
A Kiwibank spokesperson said that due to privacy laws, it would not comment on individuals.
Matthews said banks that took this action were likely to have legitimate reasons, but there was no way of knowing, and sometimes it was possible they could be acting on incorrect information or a misunderstanding.
And the customer had no way of knowing, or how they might rectify the matter.
Matthews said Kiwibank's decision might be related to its recent announcement around its responsible business banking policy.
Kiwibank chief executive Steve Jurkovich recently told Newsroom he wanted to see responsible business banking embedded in all dealings with customers.
Matthews said once a bank went down that route, it could become "a little fuzzy".
"It is very subjective and as far as I'm aware they haven't come out with any guidelines as to what they're going to accept."
Renton said she had not spoken with the bank about the decision - she received only a letter to say that by this time next week her accounts would be closed and that she was to find another bank.
"I have now moved my banking - I have no choice. How else do I pay my rent and my power and all those normal things that you pay through your banking."
She said the irony was waiting to pay tax on something she had to wait to become legal (medicinal cannabis is currently legal only if prescribed by a GP or specialist).
"So when a New Zealand bank is not prepared to support someone they've awarded for helping the needy, and they penalise them for doing that, then I think the public deserves to know what their bank is up to."
Renton said she had been open, and hidden nothing.
"I guess I could have been covert and gone offshore and done PayPal but I don't have anything to hide and I never have.
"It's not my problem the laws aren't in line with the needs."