The union claims it is currently preparing a number of legal cases to win back pay for unpaid interns, with the first case to reach court next week.
The NUJ's legal officer Roy Mincoff said following the launch of the campaign last year there has been "quite a lot" of interest from both the media and members of the union. Out of the enquiries made "a fair number" could reach court, he said.
"They had varied experiences, some got training and worked in proper conditions, with the proper rate of pay, but the majority of others reported to us they were not paid the National Minimum Wage.
"They are working, in many instances, as if they are just a member of staff and in some instances they appear to be being used as a means of cheap labour, such as being used to replace people who have been made redundant and they are effectively doing a full time job. It's really not on."
As part of the campaign, which is interested in internships of around a month or longer from up to six years ago, the union offers to potentially take on the case and provide representation for the individual and, if necessary, take it forward to tribunal.
Mincoff said even in cases where the individual had agreed to work for no pay prior to the placement, the union would still be prepared to take it on.
"It is not an even playing field at all," he said. "If somebody, by what they actually do, qualifies by the legal definition of worker or employee, they are entitled to be paid."
He added that it was also an issue of diversity, claiming those with more financial support behind them "can afford to do unpaid internships", unlike those with different financial backgrounds.
When asked if he thought the campaign this would impact on the future likelihood of media companies offering internships, he said he hoped most employers would understand.
"It's not a great deal of money. If they can't pay that much then really they are in such a state they possibly won't, or maybe even shouldn't, keep going going anyway."
Skills council Skillset produced guidelines for employers offering placement schemes in the creative industries earlier last year.
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