The price of basic foods, like bread and produce is set to rise, because of the rising cost of transporting them.
From next week road user charges increase for some truck drivers, and some may have to pass the cost on to consumers.
Under the old system, truckies were charged according to weight. The heavier the load, the more it cost them to transport it.
From next week, similar sized trucks will pay the same amount, no matter what they are carrying.
Allan Henderson harvests lettuce for a living, but he said the cost of trucking his produce will soon start growing too.
Under changes to Road User Charges (RUC), Henderson estimates it will cost him an extra $10,000 annually.
"If I filled my truck with bricks, I'm going do a lot of damage to the road, I should pay more. If I fill it with balloons, I'm doing very little damage to the road, I should pay less. Yet we're blanketed with the same cost," said Henderson.
Henderson argues his lettuce cause relatively little road damage.
Food and Grocery Council chief executive Katherine Rich says the changes will send the price of basic goods up.
"Certainly we're talking many, many millions of dollars extra cost for sending the same goods around the country," she said.
The industry's Road Transport Forum said it is an oversight.
"They almost got it right, but the bits they got wrong are causing, and will cause some serious anomalies and problems," said chief executive of the Road Transport Forum Ken Shirley.
But the transport ministry says it is fair to average out road user charges.
"We're not trying to capture money from the amount of trucks on the road. What we're trying to do is work out how much money we need to pay for the roads, then divvy it up fairly," said Ken Shirley, Financial and Economic Performance manager at Ministry of Transport.