The RMT union is preparing to ballot members over plans to operate "driver-only" trains on the new 300 million Airdrie-Bathgate line.
The union claims passenger safety would be put at risk if managers filled in as guards should a strike go ahead, and said its members were being put under "enormous pressure" to attend guard training courses.
RMT general secretary Bob Crow said: "We now have growing evidence that ScotRail are prepared to go to any lengths, and take any risks, in order to try and mobilise a scab army to break any industrial action by RMT in the dispute over the safety-critical role of guards on the new service.
"We are demanding that this bullying and intimidation of managerial and supervisory grades stops now."
ScotRail said any industrial action would cause disruption to passengers.