Democratic presidential candidate Sen. Elizabeth Warren’s latest plan could address a trend that’s making some workers’ lives miserable.

Warren has released a so-called “Fair Workweek” plan that she says would alleviate issues millions of part-timer workers face with their schedules.

Warren’s plan would require employers with 15 or more employees in certain sectors, including retail, food service, cleaning, hospitality and warehouses, to give their workers at least two weeks’ advance notice of their schedules. If changes were made to those schedules, the employers would have to compensate the affected employees and give them the right to decline to work hours that weren’t originally listed.

Warren’s plan would also stipulate that these employers must consider workers’ scheduling requests in good faith and provide a valid reason if they cannot accept the requests. Workers would also have the right to rest for 11 hours in between shifts or be compensated if that wasn’t feasible.

Warren also said she would require companies to offer qualified, part-time workers additional hours before hiring new employees or contractors. Longer-term part-time workers would also have access to benefits including family medical leave and retirement plans under Warren’s proposal.

“My aim as president will be to return power to working families and to pursue an agenda of economic patriotism that puts the interests of American workers ahead of the interests of multinational corporations,” Warren said when she announced the plan.

The National Retail Federation, the American Hotel and Lodging Association, and the National Restaurant Association could not be immediately reached for comment.

Unpredictable schedules can harm workers’ health

A recent study by researchers at the University of California-Berkeley and University of California-San Francisco examined common scheduling practices among the 80 largest retail firms in the U.S. and the toll they take on workers, based on survey data from nearly 28,000 retail and food-service workers.

“ Those who work on an on-call basis are less likely to report feeling happy. ”

“Routine uncertainty in work schedules is even more strongly predictive of worker health and well-being than hourly wages are,” the report’s authors wrote.

Workers like certainty in their schedules, Alix Gould-Werth, a senior policy analyst at the Washington Center for Equitable Growth, wrote in a report based on the study. “When workers do not know what their schedule will be, they cannot plan out their time to accommodate school attendance, second-job holding, or family obligations,” Gould-Werth added.

Workers who had more than two weeks’ notice of their schedule had a nearly 75% likelihood of experiencing happiness. But workers who had two days’ notice of their schedule or less had a 65% probability of being happy.

Also see: For desperate Americans considering a payday loan, here are other options

Improved technology means ever-changing shifts for workers

In recent years, more companies have begun implementing on-demand scheduling technology that uses data analytics on everything from customer behavior to the weather to determine how many workers are needed to operate a retail location at any given time.

As the researchers explained, this technology has allowed employers to shift their economic risk onto their employees. “Today, employees’ schedules are highly responsive to employers’ perceptions of the ebbs and flows of consumer demand,” Gould-Werth wrote. “As a result, their schedules are irregular and unpredictable.”

Given how negatively that unpredictability can affect workers’ lives, lawmakers have begun to crack down on this practice. Lawmakers in cities like New York, San Francisco and Seattle and in the state of Oregon have passed legislation requiring more predictable scheduling for workers. And politicians elsewhere, including Connecticut, are considering similar laws.

Some states (including Iowa and Georgia) have laws in place that bar local governments from adopting employer requirements in excess of state and federal laws, meaning that cities in those states cannot enact legislation that would require predictable schedules if the state doesn’t do so itself.

Some of the study’s other findings

• Only 39% of workers at the 80 largest retail firms reported having regular work schedules and, even worse, 14% of workers reported having a shift cancelled on them in the month before they took the survey.

• Half of the workers surveyed said they had to work “clopening” shifts, where they worked the closing shift the night before they had to open their store in the morning. Someone who typically works “clopening” shifts had a 67% chance of getting poor quality sleep.

• 1 in 4 retail workers said they have on-call scheduling, where they had to be available to work on certain days without any guarantee of actually being assigned a shift or getting paid. People who work on an on-call basis were 9.2 percentage points less likely to report feeling happy.

The researchers cautioned that, as always, correlation does not equal causation. There is a chance that the workers surveyed would be less happy or get less sleep regardless of their schedules.

Read more: President Trump says economic growth has benefitted women the most — but is that true?

Scheduling can be more important than salary for workers

Other research has shown that irregular scheduling disproportionately affects lower-wage workers and increases the likelihood of experiencing work-family conflict. And more predictable scheduling was associated with improved sales.

The researchers found that a worker whose pay increased from $7.25 per hour to $11.25 per hour was 1.4 percentage points more likely to be happy. That actually represented a smaller change in happiness than a similar worker would experience when they avoided a situation where a shift was cancelled.

The increased salary in question — $11.25 an hour — still falls below the living wage, meaning that while the extra take-home pay is a big deal, it won’t go as far in making the worker’s life better, according to Gould-Werth.

Put another way: The bar is already so low for retail workers when it comes to how their schedules are designed that something as simple as not having a shift cancelled can make a huge difference.

This story was originally published Feb. 20, 2019 and updated on Dec. 3, 2019.