ScotRail was today blasted by the Scottish Government for cancelling services for staff training.
Transport secretary Michael Matheson told MSPs the move which has halted dozens of trains a day was "unacceptable".
Around 50 trains were cancelled both yesterday and today because of a "shortage of train crew", ScotRail said.
ScotRail is desperately trying to ensure enough drivers and conductors are ready to run extra services being launched on Sunday as part of a major timetable change.
However, it has been hampered by new Hitachi electric trains being delivered late and delays to the refurbishment of 40-year-old diesel InterCity trains by overhaul firm Wabtec.
ScotRail is also being hit by a work to rule by members of the Rail, Maritime and Transport union (RMT) angry at not being paid the same as drivers for working on days off, which has triggered further cancellations.
Mr Matheson said such cancellations were "clearly unacceptable".
He said for ScotRail to cancel services for training was "equally unacceptable".
The minister said it was "very disappointing that passengers were bearing the brunt" for the late delivery of the trains, which was being exacerbated by the industrial action.
He will tell ScotRail Alliance managing director Alex Hynes of his dissatisfaction at a meeting this afternoon.
Conservative MSP Murdo Fraser urged him to "put a rocket" under both Mr Hynes and the RMT.
Mr Matheson called on ScotRail and the RMT to settle their dispute.
The Scotsman has been told some RMT members want to accept an improved offer from ScotRail but union chiefs are holding out for more.
The timetable changes include new Edinburgh-Glasgow services via Cumbernauld and extra local trains on the Edinburgh-Aberdeen-Inverness line.
Mr Matheson also said he "understood concerns" from passengers at plans to scrap free child travel, but it was a matter for ScotRail.
The "Kids Go Free" offer, where up to children aged five to 15 travel free with an adult will be replaced from January by "Kids for a Quid" when they will pay a £1 flat fare.
ScotRail said its new timetable "requires a significant amount of training for our drivers and conductors".
A spokesperson said: "We're sorry to our customers who have experienced disruption to their journey.
“The majority of the impact is a result of our final push to deliver the December timetable improvements, which will bring faster journeys, more seats, and more services for our customers.”