Engineers are to join thousands of railway workers on strike in the latest outbreak of industrial unrest sweeping the country.
Unite said about 350 of its members on Great Western Railway (GWR) will walk out on October 1 in a dispute over pay.
Thousands of rail workers across the country will be striking on the same day, threatening huge disruption to services.
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Delegates travelling to the Conservative Party conference in Birmingham will be among those affected.
Unite said its members in GWR were facing the third year of having their pay frozen.
Unite general secretary Sharon Graham said: “For years, the wages of our Great Western Railway members have failed to keep up.
“With rocketing prices, the value of their pay is now falling even further behind.
“Great Western Railway and its owners First Group can absolutely afford to pay a decent rise – it is simply unacceptable that they are refusing to do so while sitting on such enormous profits.
“They need to put forward an offer that reflects the rising cost of living for GWR workers.”
The striking workers are based at depots and stations in London, Exeter, Tiverton, Plymouth, Swindon, Swansea, Reading, Penzance, Oxford and Bristol.
If the dispute is not resolved then more strikes will be scheduled, said Unite.