The taxpayer will have to foot the bill of a train operator's "flat refusal" to negotiate with striking train guards, union bosses claimed.
More than 300 RMT members on the Birmingham-based Virgin Cross Country network ended their third Sunday strike last night with the company and union bosses at stalemate.
However, Virgin said it maintained a full service of 123 trains by using managers and other trained staff as guards to beat the strike.
A spokesman said the only disruption was because of engineering works around Leamington Spa in Warwickshire but otherwise it was a full service.
Virgin Cross Country said it was prepared to have pay talks with the RMT but only if it accepted productivity would form part of the discussions.
A spokesman for the company said the RMT had so far refused to accept the condition.
Members of the RMT voted for the strike action, which started on New Year's Day, over what it claimed was the "erosion" of Sunday pay rates.
RMT general secretary Bob Crow said: "Virgin Cross Country is cynically throwing huge sums of money at keeping services running on Sundays because they know that the public will eventually foot the bill.
"The cost of settling our claim works out at less than £6 per shift, yet they are paying managers an extra £100 each to cover our members' jobs on strike days.
"They were so desperate last Sunday they shelled out for a cab fare to bring a manager more than 200 miles from Plymouth to Birmingham to take charge of a train.
"Anyone in their right mind will wonder why a company is prepared to spend several times more on a dispute than it would cost to settle it.
"But Virgin Cross Country know that the public - including people who never use their trains - will be given the bill and maybe that is why the Virgin board saw fit to overrule its own management and veto the settlement we thought we had reached last summer.
"We are ready for talks at any time, but Virgin Cross Country are demonstrating a contempt for our members, for the travelling public, and even for the managers they are expecting to do our members' jobs on top of their own full working week."
A spokesman for Virgin said it was "disappointed" by the strike and added the two sides had reached stalemate over the dispute.
"If we say OK to these demands we are left with two options to pay for them." he added. "Either we go to the Department for Transport and ask them to increase our subsidy, which they are not going to do, or we put fares up for the passenger and that is something we don't want to do.
"It is difficult to understand what the RMT mean by 'eroded' Sunday pay because in 2002 they successfully negotiated a deal in which the working week was reduced by two hours but the pay remained the same. With annual bonuses as well, we don't know why this strike action has come about."