Desperate jobseekers are paying thousands of dollars to work for free, prompting calls for a code of conduct for unpaid work experience.
UnionsWA said jobseekers were being exploited, with work experience programs up to several months.
Secretary Meredith Hammat said the growing practice risked killing off some entry level jobs, as the WA jobless rate for 15 to 24 year olds hit 10 per cent.
"Individuals are having to pay to access internships and long periods of unpaid work," she said.
"If people are churned through to, in effect, avoid paying someone for real work, these practices are unacceptable and they are exploitation."
Ms Hammat said UnionsWA supported work experience connected to accredited courses or specifically for the unemployed, but wanted limits on the length of unpaid programs and more guidelines to protect jobseekers.
Under the Fair Work Act, internships must be linked to education or training, but a survey by advocacy group Intern Australia found 70 per cent were not linked to any course and only 30 per cent were structured.
The survey found 87.5 per cent of respondents had completed an unpaid internship, 61 per cent had done at least two stints, and that most lasted between two to 12 months.
Spokeswoman Colleen Chen said the internships provided valuable opportunities but there was a fine line between "gaining experience and being used as cheap or free labour".
_The West Australian _ is aware of several cases in which local students have been falsely promised jobs at the end of work experience programs lasting months.
Australian Interns, which organises work experience programs across the country, yesterday defended charging students $2000 to $5500.
Managing director Diana Van Woerkom said the fees ensured the agency could run a structured program that prevented exploitation. Their programs run from six to 52 weeks, usually for 40 hours a week, and mostly in professional industries.
Only interns in the hospitality industry worked fewer hours - 30 hours - and received some money for their contribution.
The agency places international students in Australia, and puts local students in foreign workplaces. Ms Van Woerkom backed calls for a code of practice but said it was unrealistic to ban payments for agencies that organised programs.