It comes as a new analysis found a 22 per cent difference in the pass rate at two of the country's testing centres last year
The figures obtained by Newstalk show that almost 60 per cent, or 29 of the 49 NCT centres, are booked up until the summer.
They include centres in 17 counties throughout the country.
Junior Transport Minister Jack Chambers has said it is “totally unacceptable” as the situation 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 per cent 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 per cent , while the centre at Derrybeg in Donegal had a pass rate of just 40.01 per cent .
Yesterday it was revealed how the NCT is recruiting staff from the Philippines in an attempt to relieve a backlog that has reached seven months in parts of the country.
Gardaí are now being forced to take the delays into consideration when they stop vehicles without valid certificates of road worthiness.
The vehicle inspection company has drafted in 44 testers from the Philippines, who will be assigned to test centres with the longest delays.
The NCT has also increased staff overtime and temporarily relocated 20 employees from its contractor’s Spanish operation for three months in a desperate attempt to catch up.
Gardaí also say they “are cognisant of the delays experienced by NCTS in the provision of dates for the NCT”.
An examination of the online booking system has found that centres, including Northpoint in Dublin, as well as Dundalk are currently offering August as the earliest date available for a vehicle inspection.
Other centres like Fonthill, Greenhills in Dublin are not much better, with dates in late July being offered. In other test centres such as Ballina, Galway and Donegal, dates in March are being offered.
Deansgrange in Dublin can somehow offer tests in February despite its relative proximity to other Dublin centres that have waiting times of six months or more.
Applus+, the company that has the contract to run the NCT, said every effort is being made to manage the current demand, including recruitment of additional inspectors and providing overtime to cover leave and additional shifts for staff.
It said the problems in booking delays were mainly caused by staffing issues along with a high demand for tests and the long-term impact of Covid.