The Government's plan to make greener cars cheaper could also end up subsidising vehicles with lower safety ratings, the National Party says.
But Associate Transport Minister Julie Anne Genter has accused the Opposition of "desperately scaremongering".
The Government last week proposed a policy that would see lower-emitting vehicles, and especially electric cars, discounted by up to $8000, while "gas guzzlers" would be hit with price increases of up to $3000 from 2021.
National leader Simon Bridges says many of the smaller lower-emitting Japanese vehicles that could get subsidies under the scheme had one or two-star safety ratings.
The Government is reported to be mulling a ban on lower-rated cars.