The Retail Council of Canada is warning businesses and consumers about a sharp rise in counterfeit $20, $50, and $100 bills circulating since November.
The association says more fake bills were detected in a single month than in all of last year combined, with counterfeiters using increasingly sophisticated techniques.
Retail officials say the busy holiday shopping season makes detection even more difficult, even for trained staff.
The council is calling for increased police resources and government action, noting retail theft and fraud cost businesses about $9 billion a year.