There are some 3.5 million vehicles in Greece that have not passed the regular roadworthiness test, known as KTEO.
The data was made public Thursday by the association representing private centers that conduct the KTEO tests. It said that some 2.5 million cars and 1 million motorcycles have not been checked.
Vehicles have to be tested four years after they are first registered and then every two years after that. Any owners that do not meet the deadlines are fined.
However, thanks to a law passed earlier this year there is a 50 percent reduction on the fines if the tests are carried out this year.