Shadow Chancellor Ed Balls unveiled plans to provide guaranteed jobs for the long-term unemployed if Labour were re-elected.
Writing for PoliticsHome, Mr Balls said the £1 billion scheme would see 130,000 people out of work for more than two years offered posts on at least the minimum wage.
But they face losing benefits if they refuse to take the jobs.
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The letter was signed by the CBI, British Chambers of Commerce, the EEF, the Institute of Directors and the Federation of Small Businesses.
A spokesperson said Rory Stewart's remarks were in line with the British government’s stated position.