Employees at Silicon Valley giants Facebook and Apple are not short on generous perks: extended family leave, sleek onsite medical centers for employees, free massages and candy shops.

And now, up to $20,000 in coverage for egg freezing for non-medical reasons, allowing women to potentially press the pause button on their fertility. NBC News is reporting that Apple will begin offering the perk to employees in January under its fertility benefit. Facebook began offering the coverage in early 2014 as part of its surrogacy benefit.

The two tech giants appear to be the first major companies to do so for non-medical reasons. In a sign of its rarity, neither the Society of Human Resources Management nor the Families and Work Institute, a nonprofit that does research on workplace issues, have ever asked about egg freezing as a benefit in surveys.

While the perk might seem like just another weapon in what's been called the perks arms race of Silicon Valley, it could also resonate in particular with millennial employees who are getting married and having children later than ever before. And of course, it could have an outsized effect on the trajectory of women's careers.

Advocates of the increasingly popular practice say it gives women more choice and control, allowing them to potentially put off parenthood until it's the right time for them or their careers. NBC News reports a surge in interest since the "experimental" label on egg freezing was lifted two years ago. And Bloomberg Businessweek devoted an entire cover story to the issue in April called "Free Your Eggs, Free Your Career." The article cites an NYU doctor who says the procedure has gone from five percent of his clinic's practice five years ago — when it was mostly for medical reasons among, for example, cancer patients — to a third of it now, with most being non-medical.

Yet some experts on gender and work-life issues also see potential conflicts for companies that pay for egg freezing. Joan C. Williams, a professor at the University of California Hastings College of the Law, calls it a laudable benefit as long as it's offered in the right context. "If women are asking for it, I think it makes sense to give it to them," she says. "But it shouldn't be a substitute for creating a workplace where motherhood is compatible with a high-powered career."

Facebook, for its part, subsidizes day care and gives moms and dads four months of paid leave. And Apple noted in a statement that it continues to expand its benefits for women and wants "to empower women at Apple to do the best work of their lives as they care for loved ones and raise their families."

Still, the move could be a high risk if the coverage is offered somewhere that doesn't offer other family-friendly benefits. Or, it could send the wrong signal in a culture that already only rewards people who commit to putting work above all else, says Anne Weisberg, a senior vice president at the Families and Work Institute. "If those are the signals, people will read a policy like this not as 'we want to give people more options,' but as 'this is what we expect.'"

The news made Weisberg think of how much hasn't changed since she graduated from Harvard Law School in 1985. At the time, the female law partners she spoke with had all waited until they were partners to have children, only to discover it actually wasn't any easier to wait. "It was harder physically and harder professionally," they told her.

But at too many companies, Weisberg says, putting off children is still considered the way to go. "Most organizations are still clinging to that male lifecycle model where, if you can’t have the pedal to the metal in your mid-30s to mid-40s, you’re out of the game."

Read also:

Like On Leadership? Follow us on Facebook and Twitter.