Over 400 workers across Stagecoach South West buses are balloting for strikes over the victimisation and sacking of a RMT union branch official.
The majority of the RMT members are based in Exeter with others in Exmouth and Sidmouth.
As well as drivers, the ballot includes engineers, clerks, cleaners and controllers.
The RMT said it has “repeatedly refuted the serious allegations levelled at our member by company bosses”.
The union said management “have chosen to ignore the facts” and its sacking of the official is “grossly unfair and wholly disproportionate”.
The union is urging a yes vote in the ballot that closes on the 18 May.
Unite union members working for north west London bus firm Tower Transit are balloting to strike in defence of their union rep this week, Socialist Worker understands.
It is likely there could be a high vote for action.