This helps to explain why U.S. graduates are increasingly challenging the idea that they should work for free in order to gain a foothold in the global job market — most notoriously through a series of high-profile class actions against companies including Fox Searchlight Pictures, Atlantic Records and Condé Nast.

In June this year, a federal judge in New York found that the Fox unit had violated minimum wage laws by not paying interns on the set of the film “Black Swan.”

U.S. Department of Labor guidelines state that an internship must benefit the intern rather than the employee. After the landmark Black Swan ruling, “even in the ‘sexy’ industries like publishing and media, companies are starting to take notice,” said Donald C. Dowling Jr., a junior partner in international employment law, at the New York law firm White & Case.

Mr. Perlin said the ruling — and copycat cases that have followed — may have marked a turning point. “Over 20 lawsuits, a major precedent from a federal judge, extensive press coverage, changing policies at companies and colleges, as well as new campaigns led by young people — all of these are starting to alter dramatically the culture of unpaid work and the internship economy,” he said.

U.S.-style class action lawsuits are relatively rare in Europe, even in countries where they are legally possible. Still, European protests against unpaid internships are on the rise. Organizations such as Intern Aware in the United Kingdom, Génération Précaire in France and La Repubblica Degli Stagisti in Italy collect accounts from dissatisfied interns, offer legal information and resources, organize protests, and generate press coverage.

The European Parliament itself offers a variety of unpaid positions, and in July this year a “sandwich protest” saw Brussels interns congregating to protest against unfair working conditions. The protest’s Facebook page said, “It is a fact that many interns are working without any reimbursement, without a contract, or in a framework of inappropriate payment and working hours.”

These protests are having an impact. Ben Lyons, co-director of Intern Aware, has worked with lawyers in Britain to help interns to come to private settlements with a number of high-profile companies, including the department store Harrods. Mr. Lyons said recent initiatives in Britain have included an investigation by Her Majesty’s Revenue and Customs into breaches of minimum wage laws, which has already claimed back almost £200,000, or $320,000, in unpaid wages for interns, and a new government policy, announced last month, of “naming and shaming” employers in breach of minimum wage laws.