As if poverty-skirting wages don't cause enough stress, most service workers in the Philadelphia region labor under unpredictable schedules that trigger a host of ailments and insecurities, according to a study.

About 100,000 people, most of them in part-time jobs, toil in the retail and food service sectors in the region.

Irregular hours cause many who work for hourly wages to suffer financial hardship, according to an ongoing national study, called the Shift Project, conducted by two California researchers. Workers' weekly take-home pay, already low, fluctuates dramatically. They are less likely to pay their bills. Planning for child care and other family responsibilities becomes much harder. They report more psychological distress and poor sleep quality.

"Just in time" scheduling  represents a huge trend with many retail stores and restaurants now using it to match staffing with consumer demand, said Kristen Harknett, a researcher at the University of California-San Francisco who conducted the study with her research partner, Daniel Schneider, of UC-Berkeley.

Employees receive schedules a few days in advance and may have their shifts changed or added at the last minute. About 30 percent of the Philadelphia service workers surveyed said they were expected to keep their schedules open and remain available for work.

"Companies are already under a lot of pressure to back away from some of these practices, to not rely on on-call workers and give more notice," Harknett said. "Several cities are contemplating changes."

Seattle, San Francisco, New York City, and the state of Oregon have passed legislation that requires companies to give employees advance notice of their work schedules. Some require larger retailers and restaurants to offer some payment to their hourly workers when shifts are eliminated on shorter notice.

Philadelphia City Council member Helen Gym and others in City Hall are reviewing those ordinances and considering whether to propose legislation that would require employers to give their workers more consistent schedules and more advance warning if their shifts change.

"We're actively looking at that, but there is not a specific timeline," said Gym's spokeswoman, Melissa McCleery.

Harknett, formerly a sociologist at the University of Pennsylvania, returned to Philadelphia this week to meet with members of City Council.

Businesses, however, typically don't want additional regulations. And several business groups are poised to oppose such legislation, arguing that it will tie employers' hands and lead to lost jobs.

In many ways, the experience of workers in Philadelphia resembles those in other cities, Harknett said. "The same aspects of instability play out all over the country," she said.

Harknett and her research partner, Schneider, say they have surveyed more than 40,000 shift workers nationwide in big-box stores, the big retail apparel chains, and fast-food chains.

Harknett's Shift Project collected survey data by placing ads on Facebook between August 2016 and June 2017. Ads were targeted at people who identified themselves as working for large retail and food employers.

Of the 687 workers surveyed in the region, the median hourly wage was $10.71. About 40 percent made less than $9, far under the living wage estimated to be $24.90 for a single parent with one child.

According to the study, the majority of retail and restaurant workers in the Philadelphia region — 77 percent — would like to have a more stable and predictable work schedule. Having more regular shifts, Harknett said, would make it easier for respondents to hold a second job.

An irregular work schedule sometimes causes extra stress and makes it hard to meet caregiving responsibilities for more than 70 percent of the shift workers, according to the study.