A third union is to ballot ScotRail workers on strike action after failing to receive what it describes as a “credible” pay offer.
Unite, which represents more than 300 workers at the publicly-owned railway operator, said its members could walk out in September.
The Aslef and RMT unions recently announced they will also be balloting their ScotRail staff on industrial action in a dispute over pay.
Unite said its members, who include train cleaners, engineers, ticket agents, hospitality assistants and conductors, were yet to receive a formal and fair pay offer from the employer.
The ballot will open on Wednesday and run until 20 August, the union said.
Unite general secretary Sharon Graham said: “Unite has no option but to ballot our members across all grades. Disgracefully, ScotRail has not even made a formal pay offer let alone a fair one for our members.
“Unite’s members are essential to keeping the trains running, yet many of them struggle to survive financially as they don’t earn huge sums of money. They have Unite’s full backing in the fight for better jobs, pay and conditions.”
The pay dispute comes as rail customers face continued disruption due to a pay dispute between ScotRail and its train drivers.
A reduced timetable is already in place – with only about 50% of services running on Sundays after drivers declined to work overtime.
Transport Scotland said negotiations were a matter for ScotRail and the unions, but Scottish government ministers were being kept informed.
A spokesperson said it acknowledged the desire of rail unions to “negotiate a fair settlement for their members”.
“Aslef’s recent confirmation it will return to the negotiating table later this week is welcome.” they said. “We would encourage all unions to do the same to engage in meaningful dialogue so that a mutually agreeable outcome can be reached as soon as possible.
ScotRail has been contacted for comment.