Drivers, station staff and other ScotRail workers are to be asked to vote on whether to strike in a row over pay.
The Rail, Maritime and Transport (RMT) union said it will ballot nearly 2,500 staff across Scotland on a strike and other forms of industrial action.
It said lengthy negotiations have failed to produce an offer on pay that meets the “very reasonable” demands of the workforce.
The ballot opens on Tuesday and closes on December 8.
RMT general secretary Mick Cash said: “After a long period of talks aimed at reaching a negotiated settlement on ScotRail pay, RMT reps are angry and frustrated that the company have failed to recognise the value of all its staff across the workforce who work equally hard on the front line during these dangerous times.
“RMT is looking for a decent and responsible offer to settle this dispute and the union remains available for talks.”
Alex White, ScotRail chief operating officer, said: “The RMT’s push for industrial action at a time of national crisis is wrong.
“ScotRail is proud to provide well-paid and highly skilled jobs for more than 5,200 people.”
He added: “While other transport operators across the country have cut thousands of jobs, not a single member of ScotRail’s permanent staff has lost their job, been placed on furlough or had any cuts to base salaries.
“This is thanks to the emergency funding we have secured from the Scottish Government.
“Passengers and taxpayers will not have much sympathy for any RMT-led strike action which stops doctors, nurses, care workers, and the other heroes of the pandemic from getting to their work.”
ScotRail said passenger numbers remain 80% down year-on-year because of lockdown restrictions, while at the height of the lockdown earlier this year, passenger numbers and revenue dropped by 95%.
The company said the average base salary for its train cleaners is more than £27,000, with some earning more than £36,000, while the average conductor base salary is more than £32,000.
The terms of the emergency measures agreement (EMA) with the Scottish Government, whereby the government has provided additional funding to make up the revenue shortfall to ensure staff can be paid and services can operate, mean ScotRail has not placed a single member of its 5,200 staff on furlough, cut any permanent roles, or made any changes to base staff salaries, said the company.
“Under the terms of the EMA, ScotRail can only begin pay talks with the trade unions when authorised to do so by Transport Scotland. Given the uncertainty around the public finances, no authorisation has been provided,” said a statement.