It is the first vote for industrial action to be called in Scotland by the biggest rail union since its firebrand general secretary Bob Crow died last March.
The union said the vote among “scores” of CrossCountry staff at Waverley station in Edinburgh would end on 24 February, meaning action could start on 3 March.
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CrossCountry operates some 12 cross-Border trains a day in each direction, including from Aberdeen and Glasgow via Edinburgh to Birmingham and Penzance.
The RMT said the sacking of Charlie Letham - a retail service manager who operates the catering trolley on trains - had been “wholly unjustified”.
It said he had been dismissed for “allegedly missing his revenue targets”, without taking into account his medical and personal problems.
RMT general secretary Mick Cash said: “Charlie Letham has been a loyal union member for 15 years and has done everything he can to continue working in his normal capacity.
“However, CrossCountry management decided the easiest solution was to dismiss our member despite the weight of medical evidence.
“This is not a situation that can go unchallenged and is a shocking abuse of power demonstrated by the company management.
“The RMT remains available for talks aimed at resolving this dispute.”
A CrossCountry spokesman said: “We are disappointed the RMT has chosen to ballot their CrossCountry members at Edinburgh.
“Mr Letham’s position has been carefully considered, including an extensive review with RMT representatives that looked at all the facts, together with his medical and personal circumstances.
“Unfortunately, his work as part of our catering sales team has been consistently and considerably below that of his colleagues over a long period of time, and falls short of the service we want.”