Trade union leaders reacted angrily after David Cameron said an incoming Conservative government would bring in new curbs on strikes in essential services.
He said next year’s Tory election manifesto would impose a threshold in the number of union members who have to vote in favour of industrial action for it to be legal.
The move follows a series of walkouts on the London Underground in protest over job losses and the closure of ticket offices.
The policy has been championed by the London Mayor Boris Johnson, who has suggested strike ballots should require a turnout of at least 50 per cent to be legitimate.
Supporters of the move say similar policies exist in several other western nations, but critics say many politicians fail to achieve election on 50 per cent turnouts.
Frances O’Grady, the TUC General Secretary, said: “Workers in Britain already face the toughest barriers to taking action to defend their living standards of any almost any advanced democracy. This has helped to turn our country into one of the most unequal where billionaires co-exist with food banks.
“The Prime Minister now wants to make industrial action even more difficult. This shows his readiness to take the side of employers and big business against ordinary working people.”
Mr Cameron told BBC1’s Andrew Marr Show: “In these essential services like the London Underground, the pain caused to people trying to get to work and trying to help their families by these strikes, which are often supported by a relatively small percentage of people who work for London Underground, I think is hugely damaging. So I think the time has come for setting thresholds in strike ballots in essential services.”
He acknowledged the policy could not be implemented in coalition with the Liberal Democrats, but confirmed it would be included in next year’s Tory manifesto.