In April, Newshub revealed what Consumer NZ calls disturbingly high margins supermarkets make on the food they sell - in some cases, they're pocketing more than half the shelf price.
Now, Newshub can reveal just how much those margins have grown, known in supplier circles as "margin creep".
Two long-time suppliers, who wish to remain anonymous, claimed the cut supermarkets make on their products has more than doubled since the 1990s. Both suppliers said they sell dry-packed products.
They said back then, the supermarket took 12 to 15 percent, compared to today where it sits between 35 and 41 percent.
That means if their food item sells for $1, the supermarket is now taking around 25 cents more than it was 30 years ago.
Food prices are starting to come down slightly, but the weekly shop is still almost 10 percent more expensive than a year ago.
Many suppliers told Newshub they're trying their best to keep prices down but said there's only so much they can absorb when supermarkets take such a high margin.
"It's very difficult to get suppliers to go on record because they're afraid of retribution from their supermarket clients, but we are hearing of disturbingly high margins," Consumer NZ CEO Jon Duffy said.
In April, Newshub spoke to 46 suppliers who identified gross profit margins as high as 55 percent. The vast majority told Newshub supermarkets took between 30 and 40 percent of the shelf price.
They told Newshub that they and the consumer were getting screwed.
"It is not even a negotiation. You're either coming in at their terms, or you're not coming in," one supplier said.
"It's limitless, their power is limitless," another said.
"It's disappointing, it's degrading, you know. It makes you wonder why you even bother," a third said.
After Newshub aired that story, more suppliers got in touch, with two providing information dating back to the 1990s.
They show the percentage supermarkets take on their products has more than doubled since then.
Those who represent suppliers said the shift over time has been dramatic.
"The margin for retailers' expectations on suppliers has shifted significantly. There have been some significant increases in the percentage margin delivered to the head office of the retailer," Food and Grocery Industry consultant Nick Hogendijk said.
Newshub asked the supermarkets why their gross profit margins for our two suppliers' products have gone up so much.
Countdown's owner Woolworths NZ said: "Providing information about the 1990s is not something we can do as we are a different business.
"We'd encourage any supplier who has concerns to get in touch with us," the Woolworths NZ spokesperson continued.
Foodstuffs said it couldn't respond in a valuable and accurate way to the limited and anonymous information provided.
"The margins they're making are not acceptable and we're taking action on it," Consumer Affairs Minister Duncan Webb said.
"Fairer prices are our top priority."
After a Commerce Commission probe found the duopoly was making excess profit of more than $1 million a day, the Government brought in the Grocery Competition Act, which includes a new Grocery Commissioner.
"The profit margins we know are higher than they should be, and the market study has indicated that," Grocery Commissioner Pierre van Heerden said.
Van Heerdan is asking suppliers to come to him and his 25-strong team with complaints about margin creep for them to investigate and is promising to take action if necessary.