Speaking at the GMB Conference in Brighton, to jeers and heckles from delegates, Cable admitted there was no need at present for a change to the law, but if excessive union mobilisation takes place this year, the Coalition would curb the unions' rights to strike.
At the moment, a union can impose industrial action if it secures a majority of those voting; one proposal is to require a majority of the total membership for authorisation of strike action, a more challenging target.
Andy Cook, CEO of Marshall-James, a firm of employee and industrial relations advisors, called for the Government to "rethink its threats".
Cook said: "It really does smack of a knee-jerk reaction to something the unions have been talking about for some time. To say to unions, 'If you go on strike, we will punish you with legislation', seems to really throw down the gauntlet to unions who are looking for an excuse to co-ordinate mass action across the public sector.
"The danger here is that the Government has raised this issue in a way that may influence the silent majority into action.
"There is no question that strikes actioned by a minority of the workforce or a minority of the union members within that workforce can be daft, as it allows a small number of people to cause a disproportionate amount of disruption - but industrial relations issues are wider than the law. You can use the law to prevent a strike, but there is still an issue between employees and employer that needs resolving. The only winners from anything relating to the law tend to be lawyers.
"The Government faces a series of challenges as we move through the next few months with a day of industrial action scheduled for 30 June - and then further, perhaps wider, action in the autumn. The action in the autumn has the potential to be the most serious, as the issue is public sector pensions. Pensions are the single common subject across the public sector and the unions know that it is the one thing that can mobilise action across all the unions - a situation that individual union leaders have been calling for since the change of government.
"At the centre of this is the battle for the hearts and minds of public sector workers. Without their support, the unions cannot go on strike, so the key is for Government to focus on winning hearts and minds and engage with people, not make threats to change legislation."
