Almost 60% of NCT centres have no test appointment available within the next five months, details obtained by Newstalk show.
Junior Transport Minister Jack Chambers has said it is 'totally unacceptable'.
There are 49 NCT centres throughout the country.
As of Monday evening, 29 centres had no test available within the next five months when we tried to book a test online.
They include centres in 17 counties throughout the country.
Minister Chambers said this is causing people anxiety and worry.
"The current waiting list times are totally unacceptable," he said.
"I know it's very disappointing for many people, causing anxiety and worry for people who are waiting for tests.
"People expect a proper standard of service, and it's meant to be a 12 day average wait time from Applus, who provide the service on behalf of the Road Safety Authority," he added.
As of Monday evening, nine centres had no appointment available until August.
They are in Cavan, Drogheda and Dundalk in Co Louth, Naas in Co Kildare, and five centres in Dublin.
It comes as a new analysis found a 22% difference in the pass rate at two of the country's testing centres last year.
The centre in Deansgrange in Dublin had a pass rate of 62.65%, while the centre at Derrybeg in Donegal had a pass rate of just 40.01%.
The national average pass rate at centres around the country was just over 54% - up more than 1.5% on 2021.