According to a recent study from the Economic Policy Institute, this is life for about 17 percent of the labor force. So called "just-in-time scheduling" is far more common for those who work for hourly wages or are part-time employees, or both. Part-time workers—more than six million Americans—are more than twice as likely to have unpredictable hours than full-time employees.

Many workers had one week or less of advanced notice about their upcoming work hours, the study found. Such haphazard scheduling has been linked to not only lower levels of job satisfaction, but also to greater levels of work-family conflict, according to the Lonnie Golden, the study’s author. Another study, published in the Journal of Occupational and Environmental Medicine, had similar findings, linking irregular shift schedules to diminished cognition and physical health, with workers who were exposed to such schedules for extended periods showing decreases in their ability to reason, think, and recall information.

In some cases, the differentiation in weekly work hours or varying start times may reflect a move toward increasingly flexible work places, but that's not likely the case for low-income, part-time workers, who make up such a large portion of those working with unpredictable schedules, says Golden.

Additionally, the phenomenon may be contributing to the growing economic inequality in the country, according to Golden. For example, a lack of predictable hours can lead to difficulty obtaining or keeping government benefits for some workers. A 2014 study from researchers at the University of Chicago noted that in some states, qualification for child-care subsidies are tied to the number of hours worked. That can mean that decreased hours lead to a loss of child-care benefits, which then leaves parents unavailable to work, even when shifts become available. “Work-hour requirements are based on the assumption that workers decide how many hours they work, yet because hours are a key component of labor costs, corporate policies often restrict their availability,” write Susan Lambert, Peter J. Fugiel, and Julia R. Henly, the study’s authors.

In some states, right-to-request laws, which provide such workers with the ability to ask for changes to schedules, seek to empower such workers by giving them more control over the hours they are assigned. There are other policies that seek to aid these workers, too, such as San Francisco’s Family Friendly Workplace Ordinance, which allows family caregivers to request greater schedule flexibility, and a New Jersey policy that requires non-exempt employees to be paid for at least one hour of work if they show up for work at the scheduled time, even if they are then told that they aren’t needed for their shift.