The threat of strikes on some of the country's busiest rail routes is set to move a step closer when the result of a ballot among hundreds of guards and drivers is announced.
More than 600 workers at First Great Western (FGW) have been voting on whether to launch a campaign of action after the Rail Maritime and Transport (RMT) union said industrial relations had broken down.
The union also claimed managers were being used to guard and drive trains and this had "fanned the flames" of the dispute.
RMT general secretary Bob Crow said: "There are safety implications in using managers to undertake operational duties, not least because it is unclear what level of training they have received, and now we are being told that managers are going sick at an alarming rate because of the pressure.
"Our members are now telling us that they are angry with the company's appalling behaviour and I am sure that their anger will be reflected in a decisive vote for action.
"FGW can end these disputes by talking seriously with us, but it must also agree to end what has become the routine use of managers to operate and guard trains."
Union officials are confident of achieving a vote in favour of industrial action. They will have to give seven days' notice before any strikes are held.
The train operator carries more than 60,000 passengers a day on local and long-distance services into London's Paddington station.
