Labour's claiming the Government's bungled its reforms of the ACC levies on motor vehicle registrations, but the ACC Minister says the opposition has its numbers wrong.

Labour MP Sue Moroney alleges 90,000 vehicles have been affected by wrong safety classifications, a mistake that could cost $6 million dollars in revenue.

She said the system's flawed and has seen vehicles put in the wrong safety rating without making a single improvement to road safety.

"It's a complete debacle, it's a $6 million shambles and we know now that at least 90,000 cars have been reclassified as a result of the data just being wrong."

But Nikki Kaye says the actual cost of refunds is way smaller than being claimed.

"There are about 18,000 people who have been affected. I think [Labour] said 90,000 - they said there would be 6 million and actually at the moment the figures are 578,000, but the basic point is Labour are assuming costs over a year, we record it within a month."