Almost a third of UK companies treat interns "unfairly", according to a survey by OnePoll for office space provider Business Environment.
The poll, which questioned 1,500 people, more than three in ten (31.6%) said they felt placement workers in their firm were being "exploited".
The research also revealed that more than one in seven employers (14.2%) do not give their interns the kind of work they would undertake if they managed to land the job they were seeking and (33.7%) gave interns work described as "menial".
"Internships can be rewarding and useful experiences for both the intern and the company – but a significant minority of placements are used as cheap labour, providing little experience or benefit to the jobseeker," said David Saul, chief executive of Business Environment.
"We need to recognise that internships are a two-way deal – an extra pair of hands for the company, in return for a useful experience and preferably some kind of compensation for the jobseeker."
The study also found that just two-fifths of businesses (40.3%) pay their interns the National Minimum Wage (NMW) or above.
Instead, 11.5% paid "a token amount", 5.2% simply paid compensation for travel, and 21.2% paid nothing at all.
This is despite more than two-fifths of companies (42.8%) regularly employing interns for more than three weeks at a time.
The research comes after Conservative MP Alec Shelbrooke introduced a Ten Minute Rule Motion to the House of Commons on 13 May calling for the prohibition of unpaid internships.
The Commons voted by 181 to 19 to take the motion forward. A rarity, since Ten Minute Rule Motions typically do not gain enough parliamentary support to advance.
The proposal, if passed into law, would see employers having to pay interns at least the NMW after four weeks of work.