New figures from the Society of the Irish Motor Industry (SIMI) show that car registrations fell by 1.4% in September compared to the same month last year.
SIMI said that 162 registrations decreased by 1.4% to stand at a total of 4,698 compared to September 2015's figure of 4,766.
However, total new car registrations year to date are up 18% to 143,205, compared to 120,961 the same time last year.
Today's SIMI figures also show that sales of light commercial vehicles are up 20% to 26,171 so far this year. They also showed a slight increase of 3% in the month of September.
Heavy goods vehicle registrations also recorded a 16% increase for the month of September, with registrations up 38% year to date to 2,646.
Commenting on today's figures, SIMI's director general Alan Nolan said the car industry employs 42,000 people nationwide and collects over €5 billion in taxes for the State.
He said the industry needs a Budget that supports stability and lifts consumer confidence again.
"After several difficult years it is important that the economy and our industry do not see a downward trend after the progress of this year. Consumer and business confidence are crucial in driving economic activity so any negative decisions in the forthcoming Budget will directly impact on activity, on employment and on tax revenues in 2017," Mr Nolan stated.
On the significant increase in the cost of motor insurance premiums for consumers and for businesses, he also said that SIMI wanted the re-establishment of the Motor Insurance Advisory Board as a matter of urgency.
Mr Nolan said the Competition and Consumer Protection Commission should undertake a general review of motor insurance premiums seeking to highlight the issues, including underlying costs, which give rise to the current high level of motor insurance premiums.
He noted that recent reviews of insurance costs in the UK has seen their motor insurance premiums fall to levels that are now lower than three years ago.
Meanwhile, today's figures show that over 70% of the new cars sold last month were diesel, while the top selling colour was grey.
They also reveal that the five top selling makes for the year so far are Hyundai, followed by Volkswagen, Toyota, Ford and Nissan.
The most popular car sold during the month of September was the Volkswagen Golf, while the most popular car sold so far this year is the Hyundai Tucson.