The Commerce Commission recommended the move when it completed its market study into the groceries industry in March.
It said unit pricing helped consumers make better and faster decisions about which products offered the best value, which could ultimately result in fiercer competition and sharper prices.
Major supermarkets already showed unit pricing on many products, but the commission said it had heard concerns about the clarity of the information they provided.
There have occasionally been complaints of stores and their suppliers using psychological packaging tricks to make shoppers think products might be better value than they are.
Fonterra was accused of that by an academic in 2017 when it introduced 400 gram blocks of butter in basic packaging that were cheaper than its usual 500g blocks, but more expensive on a per-kilo basis.
Fonterra Brands sales director Tim Carter rejected the criticism at the time, saying its 400g Valumetric butter blocks were “clearly labelled” and came in smaller packaging.
Clark said the new rules would require supermarkets and other large grocery stores that had a floor space of more than 1000 square metres to “clearly and consistently” display unit pricing.
“About 90% of the retail grocery market will need to display prominent, legible unit pricing that is easy for consumers to use,” he said.
Online grocery stores would also need to show unit prices and it would be required in some forms of advertising, he said.
Dairies, specialist retailers and international supermarkets will be excluded from the requirement, the details of which will be hammered out by the Ministry of Business, Innovation and Employment next year.
Clark took another swipe at supermarkets’ competitiveness when announcing the planned rule change, saying they had been “fleecing hard-working Kiwis for too long” and reiterating the Commerce Commission had estimated they were making more than $1 million a day in “excess profits”.
The Government has separately advanced law changes designed to prod Countdown and Foodstuffs into wholesaling groceries to rival retailers on more competitive terms and to make it harder for supermarket owners to use land covenants to hamper competitors.
It has also ordered a code of conduct that will be policed by a new grocery commissioner to protect supermarket suppliers from the big chains’ market power.
Early next year, the Cabinet is expected to consider whether it should consult with the public on the idea of forcing Countdown and Foodstuffs to sell some of their stores or chains to help make way for a third like-for-like competitor.
A spokesperson for Clark said he “continues to receive further advice and will make further considerations over summer”.
