The Rail, Maritime and Transport (RMT) union today announced two-day strikes from June 15 and 29 in a dispute over a manager.
The walkouts will involve maintenance staff at ScotRail’s “outbase” in Perth, where trains are refuelled and stored overnight.
New of the latest stoppages come days after the union warned of a “long summer of strike action” over a separate dispute about train conductors and ticket examiners being paid less than drivers for working on days off.
It has led to most ScotRail trains being cancelled on Sundays since last month, with the RMT saying that could continue until September.
The RMT and other ScotRail unions are also balloting their members for action in a third dispute over not being offered a pay rise without productivity improvements.
Caledonian Sleeper staff voted to strike over the issue on Thursday.
The Perth dispute is over the disciplining of a manager who was then moved to another site.
RMT Scotland organiser Mick Hogg predicted the impact of those stoppages would be “massive”, which was denied by ScotRail .
He said: “No trains would be able to get in or out of Perth as no personnel will be in attendance.
"If this was one of our members, they would be dismissed.
"It is one rule for managers and one rule for employees.
"Dignity and respect within the workplace applies to everyone.”
ScotRail engineering director Syeda Ghufran said: “I am disappointed with this outcome, despite an exhaustive investigation having taken place, in cooperation with the RMT.
“At a time when the railway faces the most serious financial crisis in its history, we need to work together to recover ScotRail, get passengers using the trains again, and build a more sustainable operation.
"Strike action is divisive and wrong.”
ScotRail said the strike ballot involved 16 people and would have “no impact on our services”.
It said an investigation which led to the dispute was “carried out thoroughly”, the union was involved throughout, and a strike ballot was “not appropriate”.