More and more workers of all income levels are expected to be on call at all times, according to a new survey, and the effects of irregular work hours are proving more harmful to families and women of color.

The findings stem from continuing surveys of 30,000 hourly workers by the Shift Project at the University of California. Researchers compared workers who earned the same wages, including at the same employers, but had different degrees of predictability in their schedules. Those with irregular hours fared worse — and so did their children, the New York Times reported.

To collect data, researchers surveyed a sample of workers at 120 of the largest retail and food service companies in the United States — industries that employ one-fifth of American workers.

According to the results, black and Hispanic women had the worst schedules, while white men had the best. The children of workers with unpredictable schedules tended to have worse behavior and more inconsistent childcare.

When it comes to workers of color faring worse than any other demographic, the researchers don’t hesitate to call it discrimination. According to the survey results, workers of color were 30% more likely than white workers to have a shift canceled in the last month. They also had more schedule instability even when they had the same education, age and other characteristics as white workers, and worked at the same companies.

Not knowing when they will work increases challenges of people living on a low income, the survey found. Those with unpredictable schedules were twice as likely to report hardships like going hungry and not being able to pay bills as those with stable schedules.

Read the full study online.