Drivers at Paddington station will be balloted for strike action unless a suspended guard is reinstated later today.
The RMT union said it would ballot all guards and drivers at the Paddington depot for strike action – which could cover the entire GWR network – unless the rail operator withdrew the suspension at a disciplinary hearing on Friday.
Rail guard and union activist Ben Frederick was suspended from duty following an incident with a member of the public at Evesham station in August and faces a disciplinary hearing.
The RMT claims Frederick was assaulted by a passenger and reported the attack to both GWR and the British Transport Police.
It said he was then suspended pending investigation of an allegation he had assaulted the passenger.
The union's general secretary Mick Cash called on the rail operator to withdraw the charges or guards and drivers would be balloted for strike action.
A GWR spokesman said: “GWR has a robust and fair disciplinary process, endorsed by all our trades unions, that will come to an evidence-based decision on any allegations made about a member of staff.
“It is right that we follow this process carefully, which includes the right to an appeal, to its conclusion.”