Sixty ScotRail services were cancelled on Friday as dozens of rail workers were forced to self-isolate under Covid rules.
Staff absences are affecting the rail firm across the central belt and passengers are being warned to check the status of their journeys before arriving at the station.
It comes as Nicola Sturgeon warned the Omicron variant could lead to a “tsunami of infections” as it quickly becomes the dominant strain in Scotland.
The First Minister said around 60 ScotRail services have been cancelled due to staff shortages, mainly because of Covid.
ScotRail said it has seen a sharp increase in staff being required to stay at home due to infections or being identified as a close contact. The number stood at 38 last week and is at 50 this week.
David Ross, ScotRail communications director, said: “We’re sorry to our customers who are being inconvenienced as a result of an increase in the number of our staff self-isolating due to Covid.
“We are working flat out to run a safe and reliable railway in difficult circumstances.”
The TSSA union said the reintroduction of the ten-day self-isolation period showed a need for the return of the furlough scheme.
General secretary Manuel Cortes said: “Sturgeon’s intervention today reinstating ten-day isolation on contact with the virus was welcome.
“But we are one island and to fight off the Omicron variant we need Britain-wide action.
“That’s why Boris Johnson needs to immediately reinstate the furlough scheme so businesses can send non-essential staff home without loss of income.”