The Department of Transport has rejected calls for greater enforcement of National Car Test regulations, saying the system is working well.
The Society of the Irish Motor Industry pointed out that there are 100,000 vehicles untested.
It has also emerged that around 30% of pre-1992 cars have not been submitted for testing.
It wants the Government to reintroduce the requirement that cars undergo the NCT examination before they can be taxed.
However, the Department of Transport has said test compliance is running at 94% and that those who avoid the test risk a €1,500 fine.
