For decades, bosses at publishing houses, glossy magazines, consulting firms, advocacy groups, movie production companies and talent agencies have groomed their assistants to be the next generation of big shots by working them long hours for low wages.

Call it the “Devil Wears Prada” economy, after the novel depicting life working for a fictionalized Anna Wintour, the longtime Vogue editor.

But now, with the Obama administration moving to require time-and-a-half overtime pay for most salaried employees making less than $47,476 a year, that business model is suddenly under assault. The change presents more than an economic challenge for the companies that rely on the willingness of young, ambitious workers to trade pay and self-respect for a shot at a prestige job down the road.

In the eyes of those who have survived the gantlet of midday coffee runs and late-night emails, the administration’s overtime regulation represents nothing less than the beginnings of a cultural shift, and not necessarily a welcome one.

“You want to bump into the boss at 8 o’clock at night,” said Dan Reynolds, chief executive of Workman Publishing, the publisher of “What to Expect When You’re Expecting” and many of Sandra Boynton’s children’s books.

“I’m interested in how this will affect that,” Mr. Reynolds said. “It’s more of a cultural thing than anything else.”

Supporters of the new rule see many benefits, saying it will rein in an overly workaholic atmosphere and perhaps diversify a rarefied world that tends to be white and upscale, thanks to its reliance on social connections and the difficulty of working for scraps without affluent parents.

Still, the coming change, which will take effect on Dec. 1, promises to be disorienting for many in these prestige professions.

In a letter to the Labor Department after it proposed the overtime rule last summer, Workman’s general manager, Jill Salayi, suggested that because the company could not afford to pay overtime to all newly eligible staff members or raise their salaries over the new threshold, it would have to cut back their hours in many cases.

“Less will be asked of them,” she argued, “which means they will not receive sufficient career development or see timely advancement and/or promotions.”

(Mr. Reynolds stressed that Workman was confident it would be able to adjust financially.)

Some high-profile nonprofits have raised similar concerns. Ideologically, the United States Public Interest Research Group, founded to fight companies that harm consumers and the environment, and Judicial Watch, which conservative activists created in the 1990s, largely to uncover Clinton administration corruption, have little in common. But both groups, in letters to the Labor Department, argued that the new overtime rule would hamper the mission of training young idealists.

“We would send them to the Clinton library if we’re doing an investigation,” Susan Prytherch, who oversees human resources for Judicial Watch, said of junior staff members. “We may think differently before sending them off.”

According to Lowell Peterson, executive director of the Writers Guild of America, East, which represents writers in movies, television and digital media, the model is very much alive and well in Hollywood as well.

“Being a writer’s assistant is often the way people get into the business of writing for a living” for television, he said.

The same goes for politics, according to Raelynn Olson, the managing partner of GMMB, which led the team that produced ads for both of Barack Obama’s presidential campaigns. “Many of the firm’s senior leaders began their careers in entry-level positions here, including a number of our partners,” Ms. Olson said.

But the problem with trying to perform one job while simultaneously demonstrating aptitude for a bigger one is that it can require extremely long hours.

At the Washington offices of Burson-Marsteller, which handles public relations and polling for a variety of corporate and political clients, so-called associates typically make $40,000 to $50,000 a year, and often work well beyond 40 hours a week. Some are tasked with pitching in on 24-hour-a-day monitoring of media coverage for clients in addition to their usual work, which can keep them up late into the night.

Under the previous federal overtime rule, which applied automatically to most salaried employees making less than $23,660, those additional hours were essentially uncounted, making the young associates a relative bargain. (Employees making more than this can be eligible for overtime under a much more subjective “duties” test, but often don’t receive it.) Under the new rule, many of these staff members are to be paid time-and-a-half overtime when they work more than 40 hours a week, if their salary remains unchanged.

Catherine Sullivan, a company spokeswoman, said: “Burson-Marsteller has always paid, and will continue to pay, overtime to those who are eligible.” She noted that employees below the associate level currently do receive overtime pay and also participate in round-the-clock monitoring.

Some organizations in which young staff members are already relatively well compensated said they would probably raise salaries over the new threshold.

But the economics of that approach may be less practical at smaller companies where labor represents a larger share of overall costs. A former employee of the Wylie Agency said assistant literary agents there — usually eight to 10 in the New York office — typically earned in the $30,000s and routinely worked 50 to 60 hours a week without overtime pay.

The former Wylie employee, who spoke on the condition of anonymity because of fear of reprisals, said that there was such an expectation of long hours that anyone arriving after 9 a.m. or leaving before 6:30 p.m. generally felt compelled to email the entire office, giving a reason for being AWOL.

Andrew Wylie, who runs the agency, said he would consider paying time and a half if he asked junior staff members to work overtime, but not if they worked long hours of their own volition. “What am I supposed to do, sit at the door with a stopwatch?” he said. “I’m not going to do that.”

David Manson, a longtime television producer who has worked on such shows as “House of Cards” and “Bloodline,” said that some entry-level jobs were so widely sought after that the new overtime rule was unlikely to affect either pay or hours, at least at smaller companies.

Lauren Weisberger, the author of “The Devil Wears Prada,” based her book — which inspired a 2006 movie starring Meryl Streep and Anne Hathaway — on her tour as Ms. Wintour’s assistant at Vogue in 1999 and 2000. She said that working from 7 a.m. to 7 p.m. was typical and that her salary almost certainly put her below minimum wage on an hourly basis.

It never occurred to her to put in for overtime pay, which Condé Nast, the magazine’s publisher, provides. “I certainly would not have had that conversation with Anna; I would have had to have it with H.R.,” said Ms. Weisberger, whose latest book will be out in July. “I don’t imagine that conversation took place a whole lot.”