Two Granite City trains have been replaced with bus services, due to shortages of train crew.
The 5.30am service from Glasgow Queen Street to Aberdeen was scrapped entirely, and a replacement bus found for the journey.
However, passengers with Aberdeen as their final destination will have to stop at each station on the way.
A bus has also been laid on between Aberdeen and Dundee for the 9.04am service to Edinburgh.
Passengers will meet the train at Dundee, before carrying on to the capital.
ScotRail has warned passengers the use of road travel means journeys could take up to 30 minutes more than planned.
Both replacements are required due to a shortage of train crew.
Along with the bus replacements, passengers might be feeling the squeeze as 17 services to and from the Granite City have been forced down from four carriages to three.
This is also due to a shortage of train crew.
The rail operator has been under pressure in recent months to sort out problems with staffing levels, which it says were caused by training for a new timetable that was launched in December, however, issues have continued into the new year.
Alex Hynes, ScotRail Alliance managing director, said: “We are very sorry to our ScotRail customers for unacceptable service in parts of the country recently.”
Meanwhile, an Abellio spokesman said its focus was on “delivering the existing franchise to the highest possible standards”.