Too many professions are relying on young people doing unpaid work, a think-tank has said.
The Institute for Public Policy Research says it is unfair that school-leavers and graduates are expected to work for free in sectors like fashion.
The TUC says a third of those on work placements and internships are unpaid.
Universities Minister David Willetts says he is concerned the practice discriminates against the less well off and the government will look into it.
One in five businesses are expected to offer work placements and internships this summer, but many - especially in areas like the arts and media - will not pay those employed even though they do productive work.
Kayte Lawton, from the IPPR, said: "We have a culture where lots of sectors are relying on unpaid work and that is just not fair, both for those who have to do the work and those who do not get the opportunities, so we need a big culture shift.
"We need the big employers to lead the way on this because they have the resources and power to pay interns and make sure they have good working conditions."
'Very fine line'
Graduate Laurie Walmsley told the BBC he had worked unpaid for a year: "I did four internships in a year. I worked for a couple of charities, I worked for a broadcaster and I worked here at Parliament.
"It helped me further my career, but it was a challenge financially because I wasn't paid.
"In fact, one of the internships cost me £400 just to cover my own transport and food costs."
Not paying minimum wage to workers is a criminal offence and employment lawyer Pam Loch says "there is a very fine line between a worker and an intern or someone on work experience".
"For an employer, they have to be careful that they are not giving someone specific tasks to be carried out on a set hours basis as you would expect a worker or an employee to do.
"It's quite a task for an employer to distinguish between different categories, but if they don't distinguish between them then they could be exposed to quite significant issues."
Note of caution
Mr Willetts said the issue was being looked at: "There is a case for very clear guidance on this and if there is more we can do we will.
"There has been some advice from the Low Pay Commission and I'll look very carefully at what the IPPR is saying as well."
But Tom Richmond, from the Chartered Institute of Personnel and Development, sounded a note of caution.
"We think it's important for businesses to treat young people fairly," he said.
"However, the concern would be that if you put more pressure on businesses to pay them more, it could be they say they simply can't take on internships any more, and then we would see a drastic reduction in the opportunities available for young people."