Unpaid internships lock everyone but the wealthy out of job markets.

That's according to the directors of Call Me Intern, which has been named best documentary at the Doc Edge Festival.

Co-director Leo David Hyde made headlines when he slept in a tent to intern at the UN in Geneva.

He says only people who can afford to work for free for months can get a shot at a job through an unpaid internship.

"At the United Nations, they did a study that found that 85 per cent of interns there would not have been able to do it without Mum and Dad helping them. It basically creates a barrier for entry for those who come from more privileged backgrounds."

He says unpaid internships are slowly embedding themselves in the economy.

"We can find them now not just in the glamorous industries like media or law, but increasingly you find them in retail and construction and agriculture."

Hyde says unpaid internships lock everyone but those with privileged backgrounds out of job marketsas interns usually need financial support to get through an extended period of time without pay.

He thinks a quietly growing number of employers are treating interns as free labour, with no repercussions.

"The law is actually quite clear, it's not a legal grey zone. If you are working at providing real value to an employer, then you are an employee. I think what it will take is for a young person to raise this issue, take it to a legal level and get a clarification."