Massachusetts on Tuesday became the third state in the nation to guarantee paid sick days for workers, with voters decisively approving a sick-leave ballot initiative, 60 percent to 40 percent.

Under the measure known as Question 4, employers will have to provide their workers with one hour of paid sick time for every 30 hours they work, to be capped at 40 hours of leave for the year, starting on July 15, 2015. Workers can use the time when they're ill, injured or need to tend to a medical condition, or when a spouse, child or parent needs to be cared for.

Smaller employers in Massachusetts with 10 or fewer workers won't have to provide paid sick leave, though they will have to let workers take unpaid time off in the same situations. The measure also makes it illegal for companies to punish workers for exercising their rights under the law.

The approval of the referendum provides a boost to a sick-leave movement that's been picking up steam in recent years. The cause has drawn in not only labor unions but also groups devoted specifically to working women and mothers. No worker, advocates maintain, should have to choose between a day's pay and caring for oneself or a child.

"The win sends a strong message to legislators and candidates elsewhere about the political power of paid sick days," Ellen Bravo, executive director of Family Values @ Work, a group that pushes for state sick-leave laws, said of the Massachusetts ballot measure. "Democrats, Republicans and Independents alike didn’t just support paid sick days in Massachusetts, they demanded them."

Connecticut and California -- as well as a growing number of cities around the country -- already have similar laws on the books.

Although more employers voluntarily provide paid sick leave than they used to, the Bureau of Labor Statistics estimates that about 39 percent of the U.S. private-sector workforce has no paid sick time. Workers without it are disproportionately employed in lower-wage jobs, such as food service and retail, where companies tend to keep a tighter grip on payroll hours.

Nationally, only one in three workers in the bottom quarter of the wage scale has paid sick leave, while only one in four part-time workers does.

The food and retail lobbies, in turn, have been some of the leading critics of sick-leave proposals as they've popped up on the local level. The Massachusetts measure was opposed by several chambers of commerce and the Retailers Association of Massachusetts, which claimed that "red tape and mandate would be costly to small businesses and taxpayers."

The Massachusetts Budget and Policy Center estimated that one in three of the state's workers doesn't have access to paid sick time.

As with raising the minimum wage, Americans in general seem to back the idea of placing a sick-leave requirement upon businesses, making such proposals good fodder for voter referendums. In a recent HuffPost/YouGov poll, 74 percent of respondents said they would support such a mandate, while just 18 percent said they would oppose it. That backing included majorities of Democrats, Republicans and independents.