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A working woman who is expecting faces a litany of tough questions before giving birth: Can she afford to take maternity leave? Will her employer compensate her if she does? Will the government help stabilize her pay?

Most industrialized countries have laws ensuring that mothers can stay home to care for their newborns without losing pay. But in the United States, the only federal law that protects a new mother’s right to time off is the Family and Medical Leave Act, which guarantees that she will still have a job when she returns from maternity leave, not that she’ll be paid while she’s away.

But because the law applies only to companies of a certain size, a large swath of workers are not covered by the law, and they’re disproportionately low-income. By one measure, just four out of 10 mothers in the U.S. take maternity leave, and affordability is the biggest factor that prevents them from doing so. Yet even when employers are required by law to provide paid maternity leave, as is the case in six states and the District of Columbia, many women still choose not to take it. This could be because they can’t afford to lose overtime or bonus pay while they’re away, or it could be because they’re simply not aware of the option: Six years after California passed a paid-family-leave law, one poll found that only 36 percent of voters in the state were aware of it. And that’s in spite of the evidence that maternity leave has health benefits for babies and moms.

But forthcoming research shows that an old-fashioned institution can help solve that problem: unions. In a peer-reviewed study to be published early next year in Industrial and Labor Relations Review, a team of researchers led by the Vanderbilt University professor Tae-Youn Park found that union-represented women in the U.S. are 17 percent more likely to take maternity leave than women not represented by a union.

The study is unique in that rather than simply investigating whether unions help workers bargain for stronger benefits, Park and his colleagues looked at the role they play in influencing whether women take advantage of the benefits available to them.

They hypothesized that a working woman’s decision to take maternity leave depends on four factors: availability, awareness, affordability, and assurance. Put another way, if a woman has a paid-maternity-leave benefit available to her, she also has to be aware that the leave exists, be able to afford to take it, and be assured that she won’t risk losing hours, pay, or promotion opportunities in the long term.

Drawing from a nationally representative sample of 4,108 workers, the researchers found that women with union representation tend to take leave more often than women without union representation due to factors that aren’t typically found in nonunionized workplaces—most notably, the presence of union representatives who serve as educators and advocates, as well as union meetings and newsletters.

“Simply offering a family leave policy does not automatically mean that workers will take a leave,” Park told me over email. “The decision to take leave is very complex, and we need to better understand the factors that prevent workers from taking a leave and how to reduce these barriers.”

Though unions have suffered through a decades-long trend of declining membership and dwindling resources, they still play a key role in advocating for workers. According to the Department of Labor, union-represented workers are more likely to have access to retirement plans, life and disability insurance, child-care subsidies, and health-care benefits. And in addition to helping moms take maternity leave, unions can assist workers in more understated ways: A 2014 study found that when workers participate in union activities such as meetings and campaigns, they develop communication and self-advocacy skills that can pay off on the job.

Still, unions can’t single-handedly fix the struggles of working moms: Park found that unions don’t appear to help protect mothers from losing future wages as a result of taking leave, especially if the leave is longer than six weeks. In both union and nonunion workplaces, it seems, new moms may still face a lingering fear that taking maternity leave might dog them for years to come.

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