Examples given by Consumer NZ included a woman buying tickets to a play who was charged three extra fees on top of the ticket price: a $1.50 service fee for each ticket, $1 for printing the tickets as well as a $2.88 credit card fee.
Another example showed an island holiday to Fiji was $71 more expensive than the "from $699" price it was advertised for, once a service fee quoted by the travel agent to Consumer NZ was added.
"These charges, often called booking or service fees, are increasingly common in the travel and entertainment industries," she said.
"But they're not included in the advertised price, misleading consumers about what they actually have to pay."
Adding fees to the advertised price was known as "drip pricing", Chetwin said.
"By the time the add-ons are revealed, consumers are more likely to be committed to the purchase and less likely to shop around.
"While the Fair Trading Act prohibits misleading representations about price, it hasn't been effective at stopping drip-pricing practices."
Chetwin said New Zealand should follow the lead of countries like Australia, where companies were prohibited from advertising a component of a price without prominently displaying the total amount.
The Commerce Commission has previously recommended similar rules be included in laws here.
In a 2012 submission to the Commerce Select Committee, it said all-inclusive pricing provisions would "substantially assist" enforcement of the Fair Trading Act.
Consumer NZ is inviting people to sign its online petition to get the law changed. The petition can be found at consumer.org.nz/sneakyfees.
Consumer NZ also encouraged participants to name and shame the companies they thought had the worst sneaky fees, either in a comment on the website or via email.
