TransPennine Express has been urged to hire more drivers after being accused of an "abject failure" to run trains.
The rail operator is currently under fire for cancelling services and is facing calls to be nationalised.
Mick Whelan, general secretary of Aslef, has written to MPs criticising the company for blaming train drivers for its "abject failure" to provide the service they are contracted to deliver, and are paid "handsomely" for by the taxpayer.