An investigation by the Tories found that several shadow cabinet figures including hard-Left Treasury spokesman John McDonnell have pledged support for a hard-line trade union manifesto that includes promises to scrap a series of curbs on industrial action.
The move comes ahead of a series of strikes on the rail network planned in the New Year that are expected to pile intense misery on commuters.
A senior Tory MP warned that the policy proposals could lead to levels of workplace havoc not seen in the UK for around four decades.
Backbencher James Cleverly said: “Labour want to take us back to the days where union barons could hold the country to ransom and disrupt the lives of millions of people with militant strike action.
“Once again, it’s working people, commuters and parents who would pay the price of Labour’s reckless plans.”
The Tory investigation found that a series of shadow cabinet members have voiced support for a trade union rights manifesto drawn up by the Institute of Employment Rights, a Left-wing think tank.
The institute has published a “Manifesto for Labour Law” calling for “a shift the focus of labour law from statutory minimum rights to collective bargaining, allowing workers to organise and negotiate for higher wages and conditions within not only their companies but across entire sectors”.
Proposals in the document include legalising so-called secondary picketing that allows workers not directly involved in an industrial dispute to join pickets.
Other ideas including legalising sympathy strikes, repealing legal requirements for notice periods before walk outs and scrapping a string of regulations covering strike ballots.
The Tories highlighted remarks from Mr McDonnell, the shadow chancellor, suggesting the document was “a blueprint for the comprehensive revision of workers’ rights when Labour comes to office.”
Speaking in August 2016, he added: “Take that as a commitment from Jeremy Corbyn, myself and our administration.”
The Tories also found that shadow business secretary Rebecca Long Bailey and Labour Party chairman Ian Lavery had also spoken in support of the manifesto.
Last night, a Labour Party spokesman said: “Labour’s plans as set out in our manifesto will boost the power of ordinary workers across the country and we are proudly committed to scrapping the unfair Tory Trade Union act, which we will do in our first 100 days of government.
“Instead of undermining workers at every opportunity as the Tories do, Labour will work closely with the trade unions and employment campaign groups to develop the best policies for workers across Britain.”