John McDonnell also called for a return to collective bargaining in the workplace and announced plans to extend the policy so pay deals would be set on an industry-wide basis.
The proposals, which make up part of Labour’s key pledge to voters ahead of June’s General Election, would see the biggest shift in workers’ rights for more than 30 years.
Speaking to ITV’s Robert Peston, he said: "What’s happened in this country over the last 20 odd years is collective bargaining has declined, 80 per cent of our workforce used to be held by collective bargaining, it stands at about 20 per cent now and that’s eroded wages overall."
Labour’s plans to boost workers’ rights will include a ban on zero hours contracts, ensuring all workers are members of a union and banning unpaid internships.
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Mr McDonnell’s comments came as party leader Jeremy Corbyn addressed delegates at the National Association of Headteachers (NAHT) conference in Shropshire.
In his speech, Mr Corbyn vowed to find £3billion to plug the shortfall in school funding - but declined to specify how he would go about raising the cash.
He told delegates that his party is the only one “brave enough to fully reverse” the huge savings that schools will be required to make by 2019/20.
Wearing a Keir Hardy Society badge with the slogan ‘Socialism Peace Equality’, the Labour leader hinted that his education policies may be funded with a rise on corporation tax, but declined go into detail, saying all would be “revealed in our manifesto”.