The struggle over the working day has long been central to Marxist analysis. In chapter ten of Capital, Volume 1, Marx chronicles the various ways that capitalists and states worked to extend the working day as much as possible, from the mid-fourteenth century up through the mid-nineteenth century. The reason was simple: the longer the working day, the more capitalists could exploit workers because after paying workers a subsistence wage, all labor done for the rest of the day was a surplus for the employer.

In the 1800s, the global working class united around the demand for a shorter working day. Subjected to sixteen-hour shifts, workers first fought for twelve hours, then ten, and finally eight. In fact, the origins of May Day lay in the international campaign for an eight-hour day.

Jump ahead to 2015. Many workers are still overworked, enduring lengthy work days and workweeks, and forced overtime. But a growing number of employees also face the problem of underwork: insufficient hours on the job, and erratic schedules that change day to day and week to week.