Motorcycle registrations have plummeted by almost 18,000 in less than two years.
Motorcycle groups say the Government's ACC levy hikes are to blame.
Figures show the total number of registered bikes has dropped from 67,150 in December 2009 to 49,401 last month.
Bikers Rights Organisation Auckland president Les Mason says due to what he calls monstrous ACC levy hikes, many riders can't afford to have their bike registered year round.
ACC Minister Nick Smith says registrations were always going to fall as costs rose.
He says the large gap between accident claim costs from motorbike crashes and what's paid in levies is now closing, as a result of the increases.