Car owners are waiting an average of nearly 25 days to get an NCT appointment.
The Road Safety Authority says lead-in times have doubled since 2020, with Covid and staff shortages being blamed.
The RSA will answer questions at the Oireachtas Transport Committee this afternoon.
Mechanics from Spain and the Philippines are being flown here to try clear the backlog, with some drivers waiting up to six months to have their car tested.
Chair of the Oireachtas Transport Committee, TD Kieran O'Donnell, says staff shortages should have been predicted.
"Why has it taken them until now to recruit staff? Surely this should have been flagged months ago. You would have known that there was going to be pent-up demand post-Covid."
Deputy O'Donnell says motorists who are waiting for appointments, are worried about driving a car without a valid NCT, and are relying on the "pragmatism of insurance companies and An Garda Síochána".
He said the Transport Committee will ask the Road Safety Authority to explain what measures are being put in place to reduce wait times for National Car Tests.
