The mayor of London Boris Johnson has been branded a "Tory liar" as the dispute between managers and trade unions over the London Underground continues.
Frances O'Grady, the general secretary of the TUC, made the remark during the May Day march in London's Trafalgar Square.
"I hope we will reach a fair and just settlement," she said. "But I tell you if striking is the only way to win, then that's what we will do. That's why the TUC 100% backs the Rail, Maritime and Transport Workers in that strike action.
"I know that Boris is saying that we are behaving like union barons. This is the man who promised no ticket office would be closed. Well, I'd rather have a union baron than a Tory liar."
The rally followed a two-day strike that caused severe delays on the Tube network. The strike was called over Transport for London (TfL) plans to close the network's ticket offices.
TfL denied union claims that the plan would result in the loss of 750 jobs. Managers stressed there would be no compulsory redundancies and that 650 workers had applied for voluntary redundancy.
RMT members still plan more industrial action with a three-day strike scheduled to start on the evening of 5 May, Bank Holiday Monday.
Len McCluskey, the general secretary of Unite, also spoke at the event which honoured the memories of Labour politician Tony Benn and former RMT general secretary Bob Crow.
"We have more in common with an Argentinian worker, a South African worker, an Australian, an American, a European worker – we have more in common with them than any British boss," McCluskey said. "Because our class is fighting for the decent type of world that Bob Crow and Tony Benn lived for."