Commuters are continuing to pack on to trains despite advice to limit travel to essential journeys only.
Pictures posted on social media showed a number of busy ScotRail services.
This was despite warnings about limiting travel because of the coronavirus outbreak.
The rail operator is now running a reduced timetable and has fewer carriages available as a result of an increased cleaning regime and staff shortages.
Nicola Sturgeon said she had “some sympathy” for ScotRail as it was clear “too many people are going to work”.
The first minister has called on businesses to heed the Scottish government's advice to stop asking people to travel to places of work.
ScotRail said that with more railway workers, such as engineering staff, being impacted by coronavirus it had little option but to introduce a reduced timetable.
David Lister, ScotRail’s sustainability and safety assurance director, said: “This is an unprecedented challenge on Scotland’s railway and the revision of the timetable is very clearly aimed at providing a critical service for the key workers across the country.
“The advice for people not to travel unless absolutely necessary could not be clearer, and we urge people to follow that guidance and help us to deliver this essential service.”
ScotRail temporarily nationalised
Meanwhile, ScotRail is to be temporarily nationalised to help the service cope with the impact of coronavirus.
The Scottish government said Scotland’s railway franchise, along with the Caledonian Sleeper, would be “supported financially to be able to maintain necessary services for essential journeys”.
The move comes as the Department for Transport suspended the franchise agreements it is responsible for, transferring all revenue and cost risk to the UK government for six months.
A Transport Scotland spokeswoman said it was working with ScotRail and Caledonian Sleeper to amend their contracts accordingly.