Scammers claiming to be from the Cancer Society have been phoning people and trying to trick them into making donations they then steal.
A 92-year-old woman was cold-called on Friday by a scammer, who asked for her credit-card details.
The charitable society said it never made cold calls for donations, and the scammers were trying to capitalise on the week leading up to its annual Daffodil Day appeal.
Chief executive Claire Austen said the tactic was fraudulent and exploitative.
"Basically it's stealing from people with cancer. This is the money that goes towarda supp services for people and their famililes who go through cancer - it really, really is terribly disappointing."
Ms Austen said anyone wanting to make a donation to the society should do so through its Daffodil Day website, ANZ bank, or one of its collectors on the streets next Friday.