As for the hiring surge that upset Mr. Anthony, Ms. Coleman said, as the holidays approach, Express typically increases its part-time work force by nearly 20 percent to accommodate extended hours and the rush of shoppers.

In New York’s fiercely competitive retail world, Mr. Anthony’s experience is not unusual. Workers at Abercrombie & Fitch, Nine West and Bed Bath & Beyond told similar stories.

A 2011 survey of 436 employees at retailers in New York City, as diverse as luxury establishments on Fifth Avenue and dollar stores in the Bronx, found that half of the city’s retail workers were part-time and only one in 10 part-time workers had a set schedule week to week. One-fifth said they always or often had to be available for call-in shifts, according to the survey, which was overseen by researchers at City University of New York.

“We’re seeing more and more that the burden of market fluctuations is being shifted onto the workers, as opposed to the companies absorbing it themselves,” said Carrie Gleason, executive director of the Retail Action Project, an advocate for retail workers that helped conduct the survey and is financed by foundations and the Retail, Wholesale and Department Store Union.

That union wants more labor deals like the one it has at Macy’s flagship store in Herald Square in Manhattan. Although that store has many part-timers, the more senior workers can reserve days off and learn their schedule six months in advance.

Mr. Flickinger, the retail consultant, said companies benefited from using many part-timers. “It’s almost like sharecropping — if you have a lot of farmers with small plots of land, they work very hard to produce in that limited amount of land,” he said. “Many part-time workers feel a real competition to work hard during their limited hours because they want to impress managers to give them more hours.”

Ms. Rosser, the Jamba Juice district manager, amplified on the advantages.

“You don’t want to work your team members for eight-hour shifts,” she said. “By the time they get to the second half of their shift, they don’t have the same energy and enthusiasm. We like to schedule people around four- to five-hour shifts so you can get the best out of them during that time.”