Sarah Dillon, head of HR Legal Service, said unemployed people could be forced into taking a job in return for waiving certain workers rights, particularly in competitive job markets.
The shares for rights scheme allows workers to trade employment rights for shares in a company of between £2,000 and £50,000. Employees who take part in the scheme give up statutory rights over unfair dismissal, redundancy, flexible working and time off for studying or training.
Trade union groups have attacked the scheme and employment lawyers predict a low take-up rate.
Dillon said while employees cannot force existing employees to convert into shareholders, they can offer jobs to prospective employees with a requirement they give up some of their employment rights for shares in the company.
"If you do not have a job then the simple fact is that you have no choice but to accept those terms," said Dillon.
"With the recent protection given to agency workers, will employee shareholders become the next disadvantaged group in employment law terms?"
Dillon said the state of the economy will be one of the main barriers to this type of agreement succeeding.
"This is an age when even the biggest and most secure businesses have gone bust," Dillon told HR. "The banks suffered near collapse, Woolworths, Comet and other long-term business have all disappeared."
Dillon warned employee shareholders could be left with no protection if they give up their employment rights, and be left "holding worthless shares".
