A Starbucks barista’s job is more than just serving coffee. She also needs to be polite, even friendly, to the customers. If she does her job correctly, then maybe the customer will walk away feeling like the barista was actually happy to serve him—that it was not only her job, but a genuine pleasure. In many jobs, that sort of projected enthusiasm may just be a way of earning some additional tips on top of the employee’s base pay. But in other lines of work—including the occupations which fuel America’s growing low-wage service sector—proper emotional responses are mandatory. There’s no sure way to measure the level of emotional labor being required of the American workforce, but it does appear to be a growing trend as employers become better at extracting additional productivity from low-wage service workers.