On Monday, New York's attorney general announced that he had sent letters to 13 major retailers inquiring about their use of "on-call scheduling," which can make workers responsible for showing up at a moment's notice, or leave them without a shift just as quickly. "Such practices take a toll on workers and prevent employees from securing childcare or pursuing other job and educational opportunities," according to a post on the attorney general's Facebook page.

For Americans who work traditional nine-to-five jobs, the life of a worker with a constantly-changing shift schedule can be difficult to fathom. Employees can wind up spending time, and money, commuting to their job, only to be told to leave early, or that they're not needed at all that day. A sudden call to work can mean scrambling for child care, or turning down much-needed hours. And a constantly shifting schedule can lead to uneven earnings, with income spiking in some months and plummeting in others, making it incredibly difficult to budget. For students using part-time jobs to make ends meet, schedule changes can mean making a choice between attending class and earning enough money to pay tuition. For workers with kids, it can mean a constant struggle to find and afford child care. The problem is bigger than mere inconvenience.

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.

These policies—along with a slew of proposed legislation at both the state and federal level are certainly important. But as my colleague Alana Semuels has reported, in some cases, employees are unaware that such laws even exist, or they are skeptical that their jobs would remain secure if they made use of them.

There are additional efforts at the firm level as well, the report notes. For some Macy’s employees in and around New York City who work at unionized stores, shift schedules are set months in advance. And Walmart’s Access to Open Hours program, which gives employees more opportunities to work additional hours came about with the help of heavy lobbying by the United Food and Commercial Workers union for better schedule practices. That brings up important questions about the role that organized labor can play in efforts to help shift workers. According to Golden, unions can certainly help the effort. "There's some pretty good examples in the collective-bargaining sector where they try to get more advanced notice," he says. But he also cautions that the effort shouldn't solely be left up to such groups. "Because their presence is a little bit more diminished, we might have to go beyond unions," Golden says. "There's a strong role to be played there, but we probably need some minimum, national standard about this as well."