Consumer NZ's latest supermarket survey found items can be on 'special' so often that shoppers have good reason to question whether the discounts are real.
The independent watchdog tracked online prices for a basket of items - mostly food but also things like cleaning products - at supermarkets in Auckland and Wellington and found most of them were on special at least six times over 12 weeks.
Chief executive Jon Duffy said often retailers would emphasise the amount that an item had been discounted, for example 50 percent off.
"But if it's discounted more regularly than it's at that original selling price, at some point you have to ask - is that description becoming misleading because it's never at that price?"
At New World, loaves of Vogel's, Ploughmans and Nature's Fresh were on special 11 out of 12 weeks. At Lower Hutt Pak'nSave, Nature's Fresh bread had an "extra-low" price of $2.99 for all 12 weeks.
Duffy said when the price was reduced that often, the special price really became the usual selling price.
"We're not complaining about low prices, but when products stay at that discounted level for so long, there has to be a point where that becomes the regular selling point for that good and supermarkets should just be upfront about that."
He said stores must be offering a genuine deal, otherwise they would mislead shoppers and breach the Fair Trading Act.
Consumer NZ wants the Commerce Commission to investigate the supermarket industry.
"New Zealand has one of the most concentrated supermarket industries in the world, with two big players dominating the market. That degree of concentration brings with it the risk consumers will end up paying higher prices," Duffy said.
The Newshub vidoe attached to this story was removed on August 6. An earlier version of this story mistakenly stated the government was planning to investigate.