The Motor Trade Association says a new report shows there could be more risks to drivers than previously thought if the Government relaxes rules for warrant of fitness checks.
The Government is proposing checks of once per year instead of the current six months for cars under 12 years old.
MTA marketing general manager, Ian Stronach said the Government's research estimates the law change could lead to two deaths and a social cost of $17 million - but a report by Monash University in Australia said the effects are much wider.
Mr Stronach said this report states a law change could result in anywhere between 1 - 25 deaths and a social cost of between $9 - $192 million.
He said differences between the Government's research and the Monash report need to be addressed and explained.