If the party wins the General Election, the Tories want any strike affecting health, transport, fire services or schools to gain the backing of 40 per cent of eligible union members.

Currently, a strike is valid if backed by a simple majority of those balloted.

The party would also end a ban on using agency staff to cover for striking workers, impose a three-month time limit after a ballot for action to take place, and introduce curbs on picketing.

West of Scotland MSP Stuart McMillan told the Reporter “This is a typical Tory attack on the rights of workers that will not benefit business or the public sector one little bit.

“It’s not the rules over trade union ballots that are encouraging people to strike but the failed policy of austerity, being pursued by the UK Government, and their plans to cut the public sector back to the level it was in the 1930s.

“This contrasts dramatically to the action being taken by the Scottish Government which is establishing a Fair Work Convention with trade unions and public and private sector employers to improve work place relations, to help grow the economy, tackle inequality and protect our public services.” His concerns were echoed by West Dunbartonshire convener for Unite the union, Charlie McDonald, who said: “We’re opposed to this. It’s just another attack on the trade union movement.

“The Tory party have got no consideration for workers and workers’ rights. They never have and never will have. Big business is who they pander to.

“It’s about taking away freedoms that people have fought for over the years. To me it’s an erosion of people’s liberty.” But West of Scotland Tory MSP Jackson Carlaw said the union leaders should not be able to hold the country to ransom.

He said: “It’s only fair the rights of trade unions are balanced with the rights of the public who pay for and depend on these services.

“It is utterly wrong that some politicised union leaders can find themselves in a position where they are holding the country to ransom. A threshold will force union leaders to engage properly and secure a healthy turnout before a strike can happen – and most people would agree with that.”