Provisional safety ratings for trucking, bus and towing companies are meaningless, the Road Transport Forum says.
Under an operator rating system being introduced by the Transport Agency, companies will be given a rating of between one and five stars.
It will be based on faults found at safety inspections and specified offences.
While ratings will not be made public until late next year, operators are being given provisional safety ratings from six months of data.
But forum chief executive Ken Shirley says the provisional ratings are meaningless, as not enough data has been collected.
Mr Shirley says the scoring will give operators a false impression of how safe they are.