Consumers could be paying an extra $68 million each year in fees that retailers are adding to the advertised price of goods and services.
Consumer NZ's latest survey has found more than two-thirds of people have been stung by extra fees, paying from $5 to more than $50 for a product or service.
It said the charges, called 'drip pricing', were often called booking or service fees and were becoming more common in the travel and entertainment industries.
Chief executive Sue Chetwin said it was "misleading" consumers because the charges were not included in the advertised price.
She said the Fair Trading Act banned misleading representations about price but it had not been able to stop the practice of drip pricing.
Consumer NZ has launched a campaign calling for the Act to include rules requiring businesses to disclose the full cost of products upfront.