This blog was cross-posted from Womenstake, the National Women's Law Center's blog.

On Monday, the news broke that a pregnant woman is now leading a Fortune 500 company—an important and exciting milestone. Before being appointed CEO of Yahoo this week, Marissa Mayer disclosed her pregnancy to Yahoo’s Board. When she announced her pregnancy publicly on Monday, she praised the Board for its “evolved thinking” in hiring her anyway – that is, for not violating the Pregnancy Discrimination Act.

I’m not so sure following the law is all that praiseworthy, but here’s what made me cringe as I read the otherwise great news of a pregnant woman breaking through the glass ceiling:

Mayer told Forbes, “My maternity leave will be a few weeks long and I’ll work throughout it.”

I’m picturing a phalanx of 24/7 baby nurses, a state-of-the-art high-tech home office located in a spacious and sunny corner of a beautiful nursery, an in-house lactation consultant, a personal chef, and, don’t forget the personal trainer! As the CEO, Mayer will be free to telecommute to her heart’s content, which is not at all the situation for most working women.

Here’s a prediction from a two-time new baby mommy: even with all that, Mayer’s working maternity leave might be a train wreck. Caring for a newborn is downright exhausting and I bet that’s still true even with all the supports money can buy. Moreover, that precious time after a baby is born is special, and every family should be able to take time away from work to enjoy it, and yes, struggle through it.

That said, each woman should be free to configure work and family in whatever way she chooses. (For full disclosure, as I write this my 2-year-old is clamoring to add her two cents by typing on my laptop keyboard with her feet.) Maybe Mayer’s working maternity leave will be a hot mess, and maybe it won’t. Why do I care?

I care because Mayer’s high-profile plan could suggest to many that these days any woman who wants to can easily balance the demands of work and family—but many working women in America today do not have any paid or even unpaid family leave to care for a newborn, let alone the degree of workplace flexibility and small army of support that Mayer can undoubtedly command. Only 11% of employees today have paid family leave programs through their employers. Less than 50% are eligible for unpaid family leave under the Family and Medical Leave Act.

For most of these workers, pressing others into service to provide care for their newborn children is not an option. And low-wage workers who take necessary time away from work to care for their babies often pay the price by losing their jobs.

Some working mothers find themselves forced out of their jobs even sooner – during pregnancy. Pregnant workers in physically demanding jobs who need simple, temporary accommodations to continue working (and earning income) during pregnancy – like water breaks or a stool to sit rather than stand – are too often denied those accommodations. Rather than provide small accommodations, employers force workers onto unpaid leave or out of the job entirely.

That’s why the National Women’s Law Center supports the Pregnant Workers Fairness Act, a bill that would require employers to provide reasonable accommodations to pregnant employees.

I haven’t walked a mile in Marissa Mayer’s shoes and I can’t pretend to know what it’s like to feel the weight of shareholders breathing down your neck 28 weeks into pregnancy. But I do know that we still have only a handful of women Fortune 500 CEOs in America. If just one of this elite group stood up for paid family leave and accommodations for pregnant workers, her voice would be heard, loud and clear.

Marissa Mayer, if you do find yourself with extra time on your hands during your working maternity leave, perhaps you could spend a few minutes writing a letter in support of the Pregnant Workers Fairness Act. Or better yet, do it now. You just might find that with a new baby, your hands are full.

Click here to tell your Senator or Congressperson to support the Pregnant Workers Fairness Act.