While unpaid postcollege internships have long existed in the film and nonprofit worlds, they have recently spread to fashion houses, book and magazine publishers, marketing companies, public relations firms, art galleries, talent agencies — even to some law firms.

Although many internships provide valuable experience, some unpaid interns complain that they do menial work and learn little, raising questions about whether these positions violate federal rules governing such programs.

Yet interns say they often have no good alternatives. As Friday’s jobs report showed, job growth is weak, and the unemployment rate for 20- to 24-year-olds was 13.2 percent in April.

Melissa Reyes, who graduated from Marist College with a degree in fashion merchandising last May, applied for a dozen jobs to no avail. She was thrilled, however, to land an internship with the Diane von Furstenberg fashion house in Manhattan. “They talked about what an excellent, educational internship program this would be,” she said.

But Ms. Reyes soon soured on the experience. She often worked 9 a.m. to 9 p.m., five days a week. “They had me running out to buy them lunch,” she said. “They had me cleaning out the closets, emptying out the past season’s items.”

Ms. Reyes finally quit when her boss demanded that she also work both days of a weekend. She now works part time as a model. Asked about her complaints, the fashion firm said, “We are very proud of our internship program, and we take all concerns of this kind very seriously.”

The Labor Department says that if employers do not want to pay their interns, the internships must resemble vocational education, the interns must work under close supervision, their work cannot be used as a substitute for regular employees and their work cannot be of immediate benefit to the employer.

But in practice, there is little to stop employers from exploiting interns. The Labor Department rarely cracks down on offenders, saying that it has limited resources and that unpaid interns are loath to file complaints for fear of jeopardizing any future job search.

No one keeps statistics on the number of college graduates taking unpaid internships, but there is widespread agreement that the number has significantly increased, not least because the jobless rate for college graduates age 24 and under has risen to 9.4 percent, the highest level since the government began keeping records in 1985. (Employment experts estimate that undergraduates work in more than one million internships a year, with Intern Bridge, a research firm, finding almost half unpaid.)

“A few years ago you hardly heard about college graduates taking unpaid internships,” said Ross Eisenbrey, a vice president at the Economic Policy Institute who has done several studies on interns. “But now I’ve even heard of people taking unpaid internships after graduating from Ivy League schools.”

Matt Gioe had little luck breaking into the music and entertainment industry after graduating with a philosophy degree from Bucknell last year. To get hands-on experience, he took an unpaid position with a Manhattan talent agency that booked musical acts. He said he answered phones and looked up venues. Although he was sometimes told to make bookings, he said he received virtually no guidance on how to strike a deal or how much to charge. But the boss did sometimes ask him to run errands like buying groceries.

“It was basically three wasted months,” he said.

Mr. Eisenbrey said many companies were taking advantage of the weak labor market to use unpaid interns to handle chores like photocopying or running errands once done by regular employees, which can raise sticky legal questions.

Eric Glatt, who at age 40 interned for the movie “Black Swan,” is one of the few interns with the courage to sue for wages over the work he did.

With an M.B.A. and a master’s in international management, Mr. Glatt wanted to get into film after a previous job overseeing training programs at the American International Group, the big insurance and financial services company. For “Black Swan,” he prepared documents for purchase orders and petty cash, traveled to the set to obtain signatures on documents and tracked employees’ personnel data.

“I knew that this was going to be a normal job and I wasn’t going to be paid for it,” he said. “But it started kicking around in my mind how unjust this was. It’s just become part of this unregulated labor market.”

Mr. Glatt filed suit, accusing Fox Searchlight Pictures of minimum wage violations. The company says it fully complies with the law and provides interns with a valuable, real-world work experience.

“The purpose of filing this case was to help end this practice,” said Mr. Glatt, who now plans to go to law school. “That was more important than my working on the next blockbuster.”

Ross Perlin, author of the 2011 book “Intern Nation,” said postcollege internships used to be confined to a few fields like film but have become far more common. “The people in charge in many industries were once interns and they’ve come of age, and to them unpaid internships are completely normal and they think of having interns in every way, shape and form,” he said.

Some interns say their experiences were quite helpful. Emily Miethner, a fine arts major at Hofstra, took an unpaid position at Gawker after graduating in 2010, doing research and social media for the news and gossip site. After two months, she moved to an unpaid internship at Flavorpill, an online cultural guide.

The knowledge she gained at those places, she said, was crucial to her landing a $35,000-a-year job as social media coordinator at Sterling Publishing. “More than just the individual tasks that I did, it was being in a great company culture and meeting a lot of people,” she said, noting that she was able to work without pay partly because she stayed at the home of her boyfriend’s parents.

Xuedan Wang, known as Diana, did not have such a positive experience. Ms. Wang, who graduated from Ohio State in 2010, interned at Harper’s Bazaar, working 9 a.m. to 8 p.m. overseeing eight other unpaid interns who ran around Manhattan picking up items from various fashion houses and showrooms.

She sued the fashion magazine in February, accusing it of minimum wage violations.

“Harper’s Bazaar was my favorite magazine growing up. I was dazzled that I was going to be working there,” she said. “But it was real grunt work, lugging things around.”

Hearst Magazines, which owns Harper’s Bazaar, said its internship programs enhanced students’ educational experience and fully complied with the law.

Some people end up on an internship treadmill. Joyce Lee, who received a film degree from Wesleyan in 2010, moved to Los Angeles and did six unpaid internships, including one for Scott Rudin, a top Hollywood and Broadway producer.

Her duties included reading scripts and picking up the mail. To pay her rent, she worked at a coffee shop and handed out fliers for a taxi company.

“Scott Rudin is made of money,” she said. “I don’t think it would be so hard for him to pay five interns the minimum wage.”

A spokesman for Mr. Rudin said he could not be reached for comment.

Ms. Lee, who is now in New York making her own film and supporting herself by again working at a coffee shop, said interns deserved better.

“If I ever become a famous filmmaker,” she said, “I promise I will pay my interns.”