A transport union has balloted thousands of ScotRail staff for industrial action in a row over pay for working on rest days.
The RMT union has sent ballot papers to 3,000 members for industrial action up to and including strikes.
RMT regional officer Mick Hogg said the issue regarded pay discrepancies for working on days off.
The union is seeking pay parity with ScotRail drivers who are reported to be paid up to £300 for working on rest day while other workers recieve less.
Mr Hogg said all workers should be treated equally.
Meanwhile, a second transport union has said it has notified ScotRail of its intention to ballot members on the same issue.
TSSA General Secretary Manuel Cortes said: “Rest Day Working payments are paid to staff to compensate them for giving up a day’s rest in order to keep our railway running.
“Our railways need more than train drivers to run. Our members in ScotRail keep trains running safely from the control room and they also make sure that passengers are safe and informed.
“ScotRail are treating our members with as second class citizens.”
A ScotRail spokesman said: “We are continuing to work with the trade unions and our people to try to reach a solution that benefits everyone.
“We do not expect this to affect services.”
The train operator is recruiting 140 new workers to cut the need for rest day working and overtime.