It comes as ScotRail prepares to announce fare rises of 3.9% – slightly lower than the UK average of 4.2% – across all ticket types from next January.
The National Union of Rail, Maritime and Transport Workers Union has balloted for strike action and industrial action short of a strike after ticket collector Scott Lewis was dismissed. If successful, the union could mount the first national strike on the Scottish rail network since 2010.
ScotRail dismissed Mr Lewis for gross misconduct after accusing him of being "aggressive" and "intimidating" during an exchange with a passenger.
The union has insisted he was "following the ScotRail procedures for customer care to deal with a fare dodger".