Police in Darlington have revealed that three fake £20 banknotes have been found in the area, but they are concerned that the issue may be more widespread.
PC Graeme Hopkirk told The Northern Echo that it should be easy for firms to tell the difference between real money and the counterfeit notes by holding them next to each other.
However while the offending notes have all been of £20 worth, businesses should check everything handed in prior to cash collections, as PC Hopkirk added: "We are aware that fake £20 notes are circulating in the Darlington area. However, the issue may not be restricted solely to this value."
Firms have been advised to contact the police immediately if they receive counterfeit money, with the police representative encouraging business owners to check the standard security features to confirm a note's authenticity.
This type of counterfeiting activity is not restricted to the north east of England either, with NewsWales reporting that more than 30 fake £20 notes have been handed in by people in the Caerphilly region of Wales.
Among the security features Gwent Police urged retailers to check were the metallic thread, watermark, microlettering and holographic strip.
On a more basic level, individuals should also consider the print quality of the note and the feel of the paper, which can prove to be tell-tale factors.