Weet-Bix boxes are quickly disappearing from the shelves of Warehouse stores throughout the country.
The breakfast cereal's maker, Sanitarium, has pulled the product from the Warehouse, while keeping stocks flowing to its competitors like Countdown and Pak'nSave.
The Commerce Commission has asked for a 'please explain'.
Meanwhile, some customers were stocking up on their Kiwi favourite while it was still available at the cheaper Warehouse price.
By 12pm on Friday, The Warehouse Albany was down to 41 boxes of Weet-Bix.
And the stocks were dropping by the minute.
A customer grabbing one of the last remaining boxes said she was unhappy with Sanitarium's decision.
"They should look after people - people are struggling - not taking it away [from] where we can afford it," she said.
"It's just making it ridiculous."
Lyn had two boxes in her basket - but not for herself.
"Actually, these two are going overseas to the US, for a family member who's over there," she said.
"They love Weet-Bix."
She was disappointed that the Warehouse would no longer be able to stock the cereal.
"They should keep it going. It's a staple; everyone likes to eat it."
A big 1.2kg family pack cost $6 at all Warehouse stores.
On Friday, Countdown's online store listed the same product at $7 - but that was on special, down from $8.20.
At Pak'nSave, the price ranged from store to store, between $7 and $7.79.
New World sold a box for up to $9.29.
Some shoppers said getting rid of Weet-Bix at the Warehouse also meant getting rid of healthy competition.
"It's approximately a dollar cheaper, and a dollar can go far," one shopper said.
"If you get one dollar free on every item, you save quite a bit."
Another customer said she usually did her grocery shopping at the supermarket but bought groceries at The Warehouse if she was there anyway.
"It just means you've got to go somewhere else if you need it. You have to go to another shop, and you'll probably end up spending more money."
The Commerce Commission was taking a keen interest in Sanitarium's decision not to stock Weet-Bix at the Warehouse.
Grocery commissioner Pierre van Heerden said it was highly unusual practice for a company to pick and choose which stores bore the brunt of its supply issues.
"This is the first time I've seen in the industry that one small supermarket has been impacted in this way, and that when there's a shortage it hasn't been applied across the board."
The Commerce Commission had reached out to Sanitarium but was yet to receive a satisfactory answer.
Van Heerden said the commission would wait for the company's reply before considering any further action.
"The powers that we have are broad-ranging, and at this stage of the game, all we're interested in is getting a response from them to understand what the issues are, and once we have that, we can determine what else needs to be done."
Saturday was the last day Weet-Bix would be restocked at Warehouse stores, although many stores had already had their final delivery and some - including the Royal Oak store - were already completely out by Friday lunchtime.
Shopper Trish said she would be stocking up while she could.
"Definitely... As much as I can afford."
Sanitarium, responding to comments made by The Warehouse, said details on its commercial relationship with customers would remain confidential.
The company would not comment on its production capacities or stock levels and would not comment further.
RNZ
