One in three furloughed workers have been asked to carry on working while their employer receives funds under the coronavirus job retention scheme.
The furlough scheme allows employers to place workers on leave of at least three weeks while saving on monthly salaries of up to £2,500.
Crossland Employment Solicitors polled 2,000 furloughed employees and found that 34% had been asked to break the rules since April 2020.
One in five have been asked to either cover someone else's job or to work for a company linked to their employer while on furlough.
Around 1.1 million employers currently use the furlough scheme.
Separately, HMRC recently told the BBC that it had received 3,000 reports of furlough fraud since April, and that figure continues to rise.
Ministers have warned that employers will be committing fraud if staff are made to work while being furloughed.
Draft legislation to give employers 30 days to confess to furlough fraud is going through Parliament and could kick in from early July.
The Government plans to introduce legislation giving HMRC powers to impose penalties and to pursue directors of insolvent companies personally.
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