The threat of industrial action on the railways is spreading as workers at another train firm prepare to vote on strikes in a row over driver-only operation.
Members of the Rail, Maritime and Transport union working as guards at ScotRail are to be balloted after talks failed to resolve a dispute.
The union says it is opposed to any plans to extend driver-only operation, maintaining that guards should be in control of operating doors.
A similar dispute has broken out at Southern Rail, where a strike ballot result is due next week.
Govia Thameslink is also embroiled in disputes over the introduction of longer trains on the Gatwick Express and plans to close more than 80 ticket offices across its franchise.
RMT general secretary Mick Cash said: “Any extension of driver-only operation is a clear attack on our members’ hard-earned terms and conditions.
“RMT members should not have to face the risk of their role and responsibilities being reduced and undermined.
“There is also a very real threat to passengers of watering down and wiping out the safety- critical role of the guard on ScotRail services. That is a lethal gamble with basic rail safety.
“RMT is in no doubt that our members will stand together and demonstrate the strength of feeling across the ScotRail network during this dispute. The union remains available for further talks.”