Hundreds of motorists are ripping off taxpayers by thousands of dollars a year by pretending they own tractors.
But police fear the number of people who are dodging car registration fees could be far higher because it's difficult to detect.
3 News was with police at a drag racing event near Hamilton last night, where they were tackling the problem.
The driver of one vehicle was barely inside the gate of the Meremere event when he was pulled over by police.
“This car has been registered as a tractor,” says acting sergeant Ryan Lilleby to the driver. “Are you aware of that?”
“I plough my fields with it on the farm – hook the rotary on the back,” says the driver.
Police aren't amused. The owner is issued with a written warning.
“It's a fraud really,” says Sergeant Mark Fleming. “It’s a fraud against all other New Zealanders, but it's one which is quite difficult to detect.”
That's because the registration labels look so similar.
Police are increasingly catching people who are cheating the system in this way.
“Instead of costing them $220 to register their car, they register it as a tractor or a campervan and they pay significantly less,” says Mr Lilleby.
The organiser said he hadn't heard of the practice.
“I might have a look to see if there are any Nuffields or John Deeres racing,” says Drag Wars organiser.
A checkpoint had been set up at the drag racing earlier in the evening. Police were on the lookout for vehicles that had been illegally modified.
One car was caught with the roll case not certified, no VIN plates or identifiers on the car, exhaust systems not certified, and registered as a tractor. The vehicle was ordered off the road. The car is one of 33 at the event deemed unsafe by police.
But last night was more about education than enforcement. Normally if you're the owner of a vehicle found to be incorrectly registered, you're facing a $200 instant fine. And if you're a repeat offender, you could find yourself up in court on a fraud charge.
Police say they will continue to target motorists with illegally modified vehicles, and may even look at using a colour code for registrations to differentiate between what really is a car and what is a tractor.