Thousands of railway signal workers are to stage a series of strikes over pay, threatening travel chaos for passengers across the country.
The Network Rail workers will walk out from noon on July 21 for 24 hours and again for 48 hours from noon on July 27.
The Rail Maritime and Transport union said the strikes were called in protest at Network Rail's refusal to change a two-year deal to one.
RMT general secretary Bob Crow said the union remained available to resolve the issue but added that he could not understand the attitude of Network Rail in refusing to consider a 12-month deal.
"Network Rail has just agreed a one-year deal for over 15,000 infrastructure workers but is refusing to give 5,000 signallers the same - that does not make sense.
"The company is fixated with a 21-month deal but all it has to do is apply the figures in the offer relating to the first year and it will be acceptable to the union."
Network Rail chief executive John Armitt said: "We have worked very hard to avert industrial action -negotiating over many months, making numerous compromises and offering a deal, which the RMT executive described as one of the best in the industry."
NR said it agreed a deal with the RMT executive last month which was to be recommended to workers, but after a meeting of union reps, the executive called a referendum on the offer, which was narrowly rejected.
Further informal talks yesterday ended without agreement. The company said it was unable to meet the union's demand for a further "substantial" increase on top of the £2,500 per head rise already on offer.
Mr Armitt added: "We are striving for a railway that is affordable to passengers and offers value for money to the British taxpayer. We urge the RMT to accept that we have offered the best deal we can and that this is the end of the line for negotiations."