Local Garda are warning of counterfeit notes in circulation.
Gardai in Monaghan issued the warning after a number of fake €20 notes were passed or were attempted to be used in Monaghan town and Castleblayney.
It follows a number of similar reports across the region and in west Cavan in recent months.
Gardai are urging people to be vigilant as they say the culprits normally try to maximise their profit, which has a larger impact on businesses.
They say if anyone has suspicions of counterfeit notes being used they should contact their local Garda station.