Retail and fast food work is notorious for erratic schedules.

But new research finds hourly workers of color in the industries have more unpredictable hours and last-minute schedules than their white colleagues.

Minority workers, particularly women of color, are “exposed to the most unstable and unpredictable work scheduling practices,” according to a report published Wednesday by sociologists at The Shift Project at the University of California. “This is not desirable schedule flexibility, but rather unpredictability and instability imposed by employers.”

Minority workers in the retail and food service industries are 10% to 20% more likely than white workers to report canceled shifts, on-call shifts and “clopenings” — shifts separated by fewer than 11 hours, the researchers found. The Shift Project, which studies scheduling practices, surveyed 30,000 employees at 120 of the largest retail and food-service firms for its report.

Although 13% of white workers reported at least one of their shifts was canceled in the last month, that percentage is 30% higher among minority workers, according to the findings.

According to the research, minority workers in retail and the food service industries are also more likely to be considered “involuntary part-time workers” — that is, workers who want to work full-time but are forced to work part-time, either because their hours were cut back or they could not find a full-time job.

The researchers attributed much of the scheduling gap between minority workers and white workers to managers’ conscious or unconscious racial bias. Although 80% of hourly white workers said their managers were white, only 38% of non-white workers said that they had a direct supervisor.

‘Fair workweek’ push

The retail and food service industries employ 17% of workers in the United States, and African-American and Hispanic workers make up a disproportionate share of the employees in the sectors compared with other industries. Top companies have relied on new technology and advanced algorithms in recent years to staff their stores and warehouses.

Last-minute scheduling creates financial strain and has damaging consequences for many workers and their families. Sometimes last-minute scheduling can make it difficult to care for young children or elderly family members. It can also lead to uneven pay and make it challenging for these workers to plan ahead.

At Walmart, the nation’s largest retailer and private employer, 44% of US employees are workers of color.

Adriana Bautista, a 13-year Walmart veteran who lives in Bay City, Texas, and works part time, said she wants to work there at least 20 hours a week. She said has worked just five hours some weeks in the past.

“Walmart also schedules me at different times every week,” said Bautista, a member of United for Respect, an advocacy group that presses for changes at Walmart and supports legislation to address unpredictable schedules. “On some days, I get off at 10 pm but have to be back at 8 am It’s exhausting, but I can’t afford to decline those shifts.”

She often relies on her family for help caring for her children.

“Most of the time I leave my kids alone with my 16-year-old daughter,” she said. “No mother wants to be in that position, but often the alternative is missing out on income we need to put food on the table.”

Kory Lundberg, a spokesperson for Walmart, said the company gives workers their schedules at least two and a half weeks in advance.

Walmart also provides “core hours” — a policy that offers workers the same shifts on the same days for as long as 13 weeks — and gives workers the ability swap shifts with other workers or volunteer to pick up additional hours.

“We are proud of the scheduling options we offer associates,” Lundberg said. “These options empower our people to build a schedule that meets their individual needs.”

Target does not disclose its mix of part-time workers or the racial breakdown of its workforce. But some Target workers, including several employees of color, recently told CNN Business that their hours have dropped.

Target has denied that it has cut hours. The company previously said that existing staffers are working this year, on average, approximately the same number of hours” as they were last year and the year prior and slightly more than they were three years ago. Target has added millions of payroll hours in recent years, the company said.

Jenny Allen, a former Payless employee who lives in Tacoma, Washington, said she often worked from opening to closing time late at night and then had to come back to work early the following morning.

“I missed a lot of time with my kids,” said Allen, who is also a member of United for Respect, the workers’ advocacy group.

Lawmakers are starting to address erratic hours and volatile pay for retail and service workers.

In recent years, San Francisco, New York City, Seattle, Chicago, Washington, DC, and Oregon and New Hampshire have passed “fair workweek” laws.

On the federal level, Massachusetts Senator Elizabeth Warren and Connecticut Representative Rosa DeLauro have introduced the Schedules that Work Act, requiring retail, food service, hospitality and warehouse employers to provide schedules to their workers two weeks in advance. The bill also would call for companies to give workers more say in their own schedules and guarantee at least eleven hours of rest between shifts.

Warren and DeLauro plan to re-introduce the bill in the coming weeks.