The RMT rail union has said its members can go on strike during COP26 after a majority voted in favour of further industrial action.
The union said 84% of more than 2,000 members backed more strikes.
It added that the schedule for the ballot would allow action to take place during the global climate gathering, which begins on October 31.
The ballot will now be considered by the union’s executive.
Sunday train services in Scotland have been crippled for months as workers protest over pay and conditions.
RMT general secretary Mick Lynch said: “Today’s ballot has been forced on us by the deliberate time-wasting by ScotRail and Transport Scotland.
“This issue should have been sorted by now and we should have had a fair and just offer that recognises the hard and important work of our members.
“The result will be considered by our executive who will decide the next steps but the company should be taking full note of this massive majority for action and we remain available for talks.”
First Minister Nicola Sturgeon said last week that she hoped the dispute could be resolved before COP26.
She said: “I would strongly encourage both sides of this dispute to get back round the table and find a resolution that is in the interests of those who work in our railways.”