Two 24-hour walkouts announced by the Rail, Maritime and Transport (RMT) union yesterday are likely to affect shoppers on the busiest day before the holidays and those travelling home for Christmas, ScotRail said.
The operator, which provides 95% of passenger trains in Scotland, said the majority of its services would operate as normal, though details of its emergency timetable are only likely to become clear early next week.
The Caledonian Sleeper service, which operates between London and Scotland, is likely to be affected, with passengers being offered a transfer to other train services.
First Group, which manages the ScotRail rail franchise, has begun training managers and other back-office staff to provide cover, including those working for its rail divisions in England.
The dispute involves 2200 RMT members – four times the level involved in the last ScotRail strike in 2010 – across the company, the bulk of whom are employed as ticket collectors and conductors.
The dispute was triggered after ticket collector Scott Lewis was sacked following an angry exchange with a passenger in March. A ballot by the RMT last month returned a two-to-one vote in favour of strike action, though only 24% of the 2200 RMT members eligible to vote have backed the action.
Bob Crow, general secretary of the RMT, said Mr Lewis has been "victimised" after trying to help a passenger.
ScotRail said the timing of the walkouts was "a clear attack on the travelling public across Scotland at Christmas rather than the company".
A spokesman said: "This reeks of selfishness – designed to give those on strike extra time off and full wages."