Union leaders have warned that crucial talks aimed at heading off strikes over pensions could be hit after Business Secretary Vince Cable said that widespread industrial action could ratchet up pressure on the Government to strengthen strike laws.
The minister was heckled when he addressed a union conference despite going out of his way to stress that the right to strike was a "fundamental principle".
Several parts of his speech to the GMB annual conference in Brighton were interrupted by shouts, boos and catcalls from delegates, while some held up a banner which read: "Vince Cable not welcome - Stop Attacking Workers' Rights."
One of the final round of talks aimed at resolving a simmering row over cuts to public sector pensions is due to be held on Thursday between the Government and leaders of several unions. Some union officials said Dr Cable's warning had soured the atmosphere and made it less likely that a deal can be reached this week.
Hundreds of thousands of teachers, civil servants and other workers are being balloted on industrial action, raising the prospect of co-ordinated strikes by three quarters of a million employees on June 30 over cuts to pensions, pay, jobs and services.
Dr Cable said: "Later this month, we may very well witness a day of industrial action across significant parts of the public sector. The usual suspects will call for general strikes and widespread disruption. This will excite the usual media comments about 'a summer' or 'an autumn' of discontent, and another group of the usual suspects will exploit the situation to call for the tightening of strike law.
"We are undoubtedly entering a difficult period. Cool heads will be required all round. Despite occasional blips, I know that strike levels remain historically low, especially in the private sector. On that basis, and assuming this pattern continues, the case for changing strike law is not compelling. However, should the position change, and should strikes impose serious damage to our economic and social fabric, the pressure on us to act would ratchet up. That is something which both you, and certainly I, would wish to avoid."
GMB president Mary Turner had to intervene during the speech and ask delegates to listen, saying: "You may not like what you are hearing, any more than I do, but please listen."
Asked about the reception he had received, Dr Cable said later that it had been "perfectly fair", adding: "A bit of heckling, but you expect that."
Prime Minister David Cameron's spokesman told reporters that there were no current proposals to change the law on the right to strike, but made clear that ministers were ready to review the position if there was a wave of "irresponsible" disputes.