Drivers on London Midland trains are to strike on 23 December in a row over pay and conditions, it has been announced.
The union Aslef said its members had backed a campaign of industrial action.
Aslef official Mick Whelan said it had been trying to "harmonise the conditions of drivers" from two firms which merged to form London Midland.
London Midland said the union turned down a deal which could have achieved this.
Mr Whelen said Aslef had been negotiating for three years to get the same conditions for more than 600 drivers from the two previous franchises, Silverlink and Central Trains.
But he said the union's efforts had been "resisted by management all the way".
"Some drivers are being paid £1,200 less than other drivers for doing exactly the same job," he said.
"It is a ludicrous situation and we will be taking strike action to demonstrate the strength of feeling of our membership at London Midland."
'Open to discussion'
A spokesman for London Midland said a strike would significantly disrupt its services on 23 December.
He said the union's demands were "unrealistic and unaffordable in today's financial climate".
"Aslef is seeking a substantial increase in pay and holiday entitlement for our train drivers without any consideration of where the money to pay for this will come from," he said.
"London Midland employs train drivers from two former rail franchises with differing terms and conditions that were protected at the point of transfer."
However, he said Aslef had turned down a deal which could have harmonised drivers' existing terms and conditions "in return for productivity".
He added the company remained open to discussion as it sought a resolution but was developing plans to support passengers in the event of a strike.
The train firm operates through London, Hertfordshire, Buckinghamshire, Bedfordshire, Northamptonshire, Warwickshire, Staffordshire, Herefordshire, Worcestershire, the West Midlands, Shropshire, Cheshire and Merseyside.