Talks aimed at resolving a row over pensions which has led to strikes by train drivers ended without agreement on Thursday.
Members of the drivers' union Aslef at East Midlands Trains walked out today for the fourth time and will take two more days of action next week.
The company said it ran an improved service compared with previous strike days.
Aslef said disruption will continue next week after the talks failed to reach any conclusion.
General secretary Mick Whelan said he was "very disappointed" that the company had come to the negotiations "without flexibility, without fresh ideas and without serious intent to end the dispute".
Clare McCartney, human resources director for East Midlands Trains, said: "This is a strike over nothing. The average driver will lose around £1,200 in pay by following Aslef's misguided call for six days of strike action.
"We do not believe it is right to force drivers to pay £500 a year more in pension contributions than independent experts and the scheme's trustees say is needed."
Aslef argues that pension contributions should not be reduced during the uncertain economic climate.
The company said it had put forward constructive proposals aimed at ending the dispute and reassuring employees on the future of their pensions.
"However, the union has failed to take up the offer, which would have put hundreds of pounds into the pockets of all employees with no loss of pension benefits," said a statement.
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