There will be a rail strike this weekend after talks with First Great Western workers failed to reach agreement.
Members of the RMT union at the rail company are due to walk out for three days from Saturday in a row over new trains.
The move is expected to disrupt the services by the operator, which runs trains out of London Paddington to Oxford, Reading and the Westcountry.
General secretary Mick Cash said in a new circular to members that urgent talks had been held with the company, but no agreement had been reached.
A First Great Western spokesman said: “We have once again reiterated that our proposals do not involve running the new trains without a qualified train manager on board and that our plans mean recruiting at least 100 more on-board staff, not less.
“Following the discussions we have written to the RMT for them to formally consider our current proposals.
“We hope to hear from them soon, and have scheduled further discussions later this week.”
Rail minister Claire Perry said: “This dispute is about replacing old trains from the 1970s with brand new high-speed Hitachi trains.
“We’re going to see more trains, more seats and faster journeys for customers, so it is ridiculous that the union bosses’ reaction is to call for industrial action and disrupt rail services for the public.
“I want to see sense prevail and for this strike to be called off as soon as possible.”