An Auckland Pak'nSave supermarket has been charged after an undercover sting allegedly caught it overcharging customers.

Kennedy's Foodcentre Limited, trading as Pak'nSave Mangere, faces 12 charges under the Fair Trading Act for alleged price discrepancies between prices advertised and the price charged at the till.

The Commerce Commission alleges that on six occasions during June and October 2018, the Mangere supermarket charged a higher price at the checkout for one or more items than what was advertised on the shelf.

The price discrepancies were raised with customer service staff at Mangere Pak'nSave following findings from a mystery shop. Commission staff returned the next day and re-purchased the same items to find the price discrepancies were still occurring.

Pak'nSave is known for its no-frill supermarkets offering competitive prices. The chain's policy "New Zealand's lowest food prices" is often pushed in its advertising jingles.

The commission said the promotional pricing was advertised online on Pak'NSave website and on price tags and signs in stores.

The charges arose from finding the price discrepancies were still occurring. The matter is now before the courts.

Foodstuffs, which operates the Pak'nSave supermarket chain, along with New World and Four Square chains, has been contacted for comment.

Each Pak'nSave supermarket is individually owned, Foodstuffs licences the operation of supermarkets through a franchise arrangement.

Michael Kennedy, owner-operator of Pak'nSave Mangere, acknowledged the charges over "pricing issues" at his store.

"We take pricing and getting it right extremely seriously. As soon as we were aware, immediate steps were taken to minimise the chance of this happening again, including additional training in-store," Kennedy said.

"We try not to make mistakes, but if we do, we always work to correct them."

The commission was unable to comment further on the matter.

The Herald understands Mangere Pak'nSave is not the only store in the supermarket chain to have had alleged price discrepancies in the past. It is understood that price discrepancies between prices advertised and those charged at the till had also occurred at a store in Thames.

A spokeswoman for Foodstuffs North Island said the company took the accuracy of its pricing in its franchised stores "very seriously".

She said the business had a "variety of systems in place" to ensure prices accurately reflected prices advertised and shown on supermarket shelves, including "internal training processes, compliance manuals and price integrity managers who assist with the process".

"Owners, and staff, are reminded regularly of the need for accuracy," she said.

"While we understand ticketing issues can occur and are usually a result of human error, this case is a reminder of how important it is to ensure accuracy between the shelf price and the till price, particularly with items on promotion. Owners and their teams know how important it is we get it right."

There are 45 Pak'nSave supermarket throughout the North Island.