Consumer New Zealand is asking the Commerce Commission to investigate whether supermarket promotions are breaking the law.
Consumer NZ chief executive Jon Duffy says sometimes deals in Kiwi supermarkets are too good to be true.
"Some of this discounting could be misleading," he told The AM Show.
"Especially when products are left on special for extraordinarily long amounts of time and they never really return to the price they're supposed to be discounted from.
Duffy says he has laid a complaint with the Commerce Commission to investigate whether this practice breaches the Fair Trading Act.
"It's quite hard to tell to be honest."
His other concern is loyalty cards - since New World rolled out its Clubcard in 2016, checkout staff have been able to swipe a card if a customer didn’t have their own. However, staff are no longer allowed to do this.
"I was caught out by this myself recently," Duffy said.
"New World has claimed they put out a lot of information about this change but if they only put out the information to people with the cards then a lot of people are missing out on the deals they thought they were entitled to."
While customers could just sign up for a card, Duffy says that also means they have to sign up to share personal data with the supermarket and third parties.
"Requiring customers to sign up for a Clubcard to get deals checkout staff used to give them anyway, sounds to us a little bit like a data grab."