Train guards and drivers on the First Great Western network have voted to embark on industrial action, union officials have said today.
The RMT said a ballot of the network's drivers and guards on its books had resulted in a comprehensive decision to strike.
According to the union, 81.6 per cent of drivers were in favour of strike action, while 71.1 per cent of guards supported it.
In addition, 88.2 per cent of drivers and 89.5 per cent of guards voted for action short of a strike.
The dispute centres on unhappiness among staff about the way managers have been required to act as drivers and guards on trains, with the union claiming such procedures impacted on safety.
"RMT members at First Great Western have today made quite clear what they think of First Great Western's confrontational style of management," RMT general secretary Bob Crow said.
"The votes reflect the anger that our members feel at the company's behaviour, and if it wants to avoid industrial action it should begin to deal sensibly with the range of issues involved and stop the routine use of managers to guard and drive trains."
Almost 300 RMT members took part in today's vote. First Great Western operates commuter and regional services across the former Wessex Trains, First Great Western Link and First Great Western routes, with many services running to and from London Paddington.