Rail workers on First Great Western are to stage a series of strikes, including over the August Bank Holiday weekend, in a long-running row over new trains.
Members of the Rail, Maritime and Transport union, including drivers and guards, will walk out for 24 hours on August 23 and for 72 hours from August 29.
Other union members who work on maintenance will strike on August 29 and 31.
The union is in dispute over the introduction of new Hitachi inter city trains, saying the role of guards will be reduced and buffet cars' facilities removed.
RMT general secretary Mick Cash said: "Despite strenuous efforts by our negotiators we have not been able to secure the kind of progress required in the key areas of jobs, services and safety for us to reach an agreement.
"As a result we have no option but to put further action on.
"The fact remains that if it is good enough for East Coast, using the same trains, to meet the very basic assurances sought by this trade union then it is good enough for First Great Western as well."
Union members staged a 48-hour strike last month which disrupted services at FGW, which runs trains to and from London Paddington, South Wales and the South West.
Mr Cash said union members were "united and determined" to continue campaigning.
The RMT said it had not been given assurances on job protection for engineers, the proposed introduction of driver-only operations would dilute the role of guards and platform staff, and buffet/restaurant facilities would be removed.
Officials said they had been given the assurances they were seeking when similar trains are introduced on the East Coast.