Train drivers are to stage three days of strikes during the Olympics in a row over pensions, threatening disruption to spectators travelling to the Games.
Members of the Aslef union on East Midlands Trains will take industrial action on August 6, 7 and 8, when a number of athletics finals will be held in the Olympic Stadium.
The company, owned by transport giant Stagecoach, said the public will be "shocked and angry" that strikes are being planned at a time of "great national pride" for the country.
David Horne, managing director of East Midlands Trains, said: "This is yet another example of Aslef playing games and is a real kick in the teeth for our customers and the country.
"The fact is that there was only one point of clarification still under discussion with the union on the pension proposal we put forward back in June. We were in talks with Aslef to deal with this issue when we heard the news that further strike action dates had been announced.
"We're particularly surprised that Aslef has announced further strike dates, rather than putting the offer that was accepted in principle back in June to their members for consideration.
"We're certain that the public will be shocked and angry to hear that the union has announced strike action during a time of great national pride for our country. We hope Aslef can see sense and call off this unnecessary strike action.
"However, if the planned strike action does go ahead, we will be pulling out all the stops to ensure that people can still travel by train and enjoy this once-in-a-lifetime experience."
The drivers staged six strikes in May in protest at changes to their pensions but called off two further stoppages in June to allow further talks.
Aslef is protesting at plans to reduce pension contributions, a move which has been accepted by other unions with members on East Midlands Trains.
General secretary Mick Whelan said: "To cut pension contributions in the current climate is highly irresponsible. It is widely believed that the fund's assets have dramatically decreased since the last valuation.
"Also, any suggestion that drivers would save money ignores the fact that the pension scheme is split 60/40 between the employer and the employee - so if our members are saving £500, the company is saving £750. In total that's £1,250 a year less going into the fund per active member.
"This is simply storing up trouble for the next valuation and the future of the scheme. It is disingenuous to suggest our members are getting something for nothing.
"The current owners of the East Midlands Trains (EMT) franchise may have no responsibility over the pension fund in a few years, whereas our members face the prospect of either cripplingly high contribution rates or reduced benefits due to a short-term cost-cutting decision made by EMT that has left the scheme in deficit."
Around 400 drivers work at the company, which said it would go ahead with planned talks with Aslef tomorrow to try to avert the strikes.
EMT said a recent pensions review found that extra payments made in recent years were no longer required, so that employee contributions could be reduced from 10.5% of pay to 9.08%, while the company would pay around £700,000 a year less.
The train operator said current payment levels were unnecessary and would mean staff paying hundreds of pounds extra for no more benefits.
"The union is trying to force through more expensive contributions than are needed which risks making the scheme unaffordable so that people drop out," the company said.
Transport Secretary Justine Greening said: "If there were an Olympic sport of self-interest, Aslef union leaders would win it hands down.
"This strike threatens Team GB's ability to plan travel from their UK base in Loughborough and would disrupt journeys for thousands of commuters and spectators.
"Ed Miliband needs to get a grip on his union paymasters so they call off this damaging and unnecessary strike."
Members of the Rail, Maritime and Transport (RMT) union on South West Trains have voted to take industrial action short of a strike in a row over an Olympic bonus, but rejected strikes by a narrow margin of four votes.
General secretary Bob Crow said: "Our members have been consulted by the union in this democratic vote and by the narrowest margins have opted not to take strike action but have voted by a significant margin for action short of a strike and the position will now be considered further by the union's executive with any further statements issued in due course."
Voting by RMT members on Greater Anglia in a similar row has been halted due to a legal challenge from the company, the union said.
Tim Shoveller, managing director of South West Trains, said: "Commuters and Olympic spectators will be rightly pleased to hear that their services during the Games will not be affected by an RMT strike.
"We're pleased that most of our employees have voted against taking a strike during the Games. This means we can deliver our full Olympic train service and ensure our passengers can enjoy the excitement of London 2012, a once-in-a-lifetime experience, without the threat of a strike.
"As we have said all along, the RMT agreed to a generous pay deal some months ago, which covered the period of the London 2012 Games. It's very disappointing that the RMT has been trying to go back on this deal and cause disruption at such an important time for our customers and our country.
"We are still waiting to hear confirmation from the RMT whether any action will be taken, but regardless of this, we are looking forward to running a full service for our passengers during the Games."