Shoppers have been overcharged for their groceries at 70 North Island supermarkets today.
Foodstuffs confirmed a technical issue led to about one quarter of "new special prices" at Pak'nSave, New World and Four Square supermarkets failing to register at the checkout.
The technical issue lasted seven hours between 7am and 2pm, and meant some customers missed out on advertised discounts.
One Pak'nSave Silverdale shopper said she had specially gone to the store to pick out a wide range of specially discounted products.
However, she only noticed a printed out sign saying "our prices may not be scanning accurately" once at the checkout and halfway through scanning her "weekly shop".
The woman asked the attendant what the sign meant and how would she know if she'd been overcharged.
But the attendant told her it was only her second day on the job and she didn't know about the pricing issue.
"I thought, 'Are you kidding me'.
"If people are on a budget and have been going through getting all the specials but they are not being rung up as specials - it doesn't sit well with me."
Foodstuffs head of corporate affairs Antoinette Laird apologised "to any customers who shopped with us in the North Island between 7am and 2pm today and didn't receive the correct special price they were expecting at checkout".
She encouraged them to contact the store where they shopped, "so this can be put right".
She said Foodstuffs took getting its prices right "extremely seriously".
"Pricing issues, such as this one, are extremely rare and we have systems and processes in place to identify them early," Laird said.
"As soon as the issue was identified this morning, our IT team investigated and rectified this within a few hours."
A Consumer NZ spokeswoman said retailers could not mislead consumers about prices.
"If a problem with the supermarket's computer system means customers may have been charged more than the advertised price, the store needs to act quickly to fix it," she said.
"It also needs to alert customers to the problem and refund anyone who has been overcharged."
She said anyone who shopped at one of the affected stores should check their receipt.
"Request a refund if you find you've paid more than you should," she said.
However, the Pak'nSave Silverdale shopper questioned how shoppers would know whether they had been overcharged.
She said she would need to return to the supermarket and go back through the aisles checking the advertised discounted prices against those listed on her receipt.
"But who has time for that," she said.
She said even if shoppers had been overcharged a small amount each, that could quickly turn into a big profit for Foodstuffs if it was spread over a large number of customers.
She thought the supermarket could have given customers a 10 per cent discount to offset any possible overcharging.
"That is what I go to Pak'nSave for to get the specials," the shopper said.
"And then you get to the checkout and it was like, 'Hey wait a second' ... I was bewildered."