Consumer NZ's latest supermarket survey found products can be on "special" so often shoppers risk being misled about the savings they're getting.
Consumer NZ chief executive Jon Duffy said price promotions had become so common that shoppers had good grounds to question whether the discounts were real.
In this year's survey, Consumer NZ tracked online prices for a basket of 22 grocery items for 12 weeks at Countdown, New World and Pak'nSave stores in Auckland and Wellington.
"Many of the items we tracked were routinely discounted. While genuine price promotions are good for consumers, we found specials aren't always as 'special' as supermarkets would like us to believe," he said.
At Pak'nSave, the majority of the 22 products that Consumer NZ tracked were on special six or more times. At New World, half the items were on special on six or more occasions.
Countdown's specials varied: anywhere from two to 10 items were on special each week.
Mr Duffy said when the price of a product is regularly reduced, the special price is really its usual selling price.
At New World, Vogel's, Ploughman's Bakery and Nature's Fresh loaves were on special 11 out of 12 weeks. At Pak'nSave Lower Hutt, Nature's Fresh bread had an "extra-low" price of $2.99 for all 12 weeks.
Stores enticing customers with price promotions must be offering a genuine deal. Otherwise, they'll mislead consumers and breach the Fair Trading Act.
Mr Duffy said supermarkets use a confusing array of terms in their price promotions, which makes it harder for shoppers to gauge whether they're getting a genuine discount.
Consumer NZ wants the Commerce Commission to use its market study powers 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," Mr Duffy said.
Despite the high degree of market concentration, the supermarket sector had failed to attract much scrutiny. Mr Duffy said it's time for that to change.