Police in Auckland are trying to find whether there is a link between three separate incidents over the last few months of fake banknotes being used in North Shore.
Police said a man paid for a coffee at a supermarket on Tuesday with a counterfeit $100 bill, but they are yet to find and identify him.
A fake $50 note was used at a butcher shop just before Christmas, and at a Glenfield clothes shop in October.
A 21-year-old woman has been charged with misusing a document in the clothes shop incident but police don't know where that note came from.
In November the police in the south of city warned about counterfeit $50 and $100 notes circulating through that area.
Officers said at the time the genuine notes were made of a polymer which was quite tough, difficult to tearand water-resistant, whereas counterfeit paper notes were easier to tear and not water-resistant.
Police say knowingly passing a counterfeit note is a crime and potentially punishable by a lengthy prison term.