They would also "close the door" on weight-based evasion - operators underestimating the weight of a vehicle and purchasing incorrect licences, the spokesman said.
Hudson said the changes unfairly affected companies like Provida Foods, whose trucks carried loads much lighter than the maximum weight allowed.
"They're going to calculate [charges] on what you might do rather than what you actually do," he said. "They talk about it being user-pays and fair but it's not fair."
He said Provida Foods' 50 trucks carried a lot of "fresh air" as a clear walkway in the back of the vehicles allowed drivers to gain access to the products being transported.
The company - which employed 110 staff across three operations in Auckland, Hamilton and Mt Maunganui - did not have the freedom to pass on the $200,000 increase in annual costs to its customers, Hudson said.
He said a "six wheeler" truck carrying the maximum axel load of 22.4 tonnes would go from paying $537.74 per 1000km to $353 per 1000 km, a 34.4 per cent saving, after the changes were introduced.
"These [heavy] vehicles are hammering the hell out of our roads," he said.
Freightways managing director Dean Bracewell said he was also disappointed with the changes, which would result in a more than 20 per cent rise in costs for the company's inter-city line haul fleet.
"[The changes] unfairly penalise those operators that don't reach maximum utilisation on their vehicles," Bracewell said.
The Ministry of Transport spokesman said the new system would benefit some transport operators more than others.
Despite being told of Hudson's calculations on the cost savings vehicle operators hauling the heaviest loads would enjoy, the spokesman said: "It is a fair system because similar vehicles pay similar charges and heavy vehicles as a group will keep paying the same amount as present to cover the cost of the road damage they are responsible for."
The spokesman said it would be up to individual transport firms to decide how they adapted to the new system and whether they passed on any increased costs to their customers.
New Rules
Current system: Transport operators estimate the actual gross weight they will carry and pay licensing fees based on that estimation.
From next month: Operators will be assigned a permanent weight classification based on a vehicle's maximum allowable on-road weight, regardless of the weight of their freight.
Opposition: Some freight players say the changes will unfairly benefit the transport operators carrying the heaviest loads that do the most damage to roads.
