Amazon is joining the throng of companies expanding their parental leave benefits for employees.

On Monday, the online retail giant said in a memo to employees that, starting Jan. 1, it would be expanding the number of weeks it offers new parents, as well as offering an unusual "leave share" program that allows employees to share their benefit with a spouse or partner. Amazon's founder and CEO, Jeff Bezos, also owns The Washington Post.

Under the new policy, Amazon now offers birth mothers up to 20 paid weeks of leave, including four weeks of paid pre-partum medical leave, 10 weeks of paid maternity leave, and six weeks of paid parental leave. That six weeks of paid parental leave is also available to new fathers as well as all other new parents who have been with the company at least a year. The company said the benefit would be available to full-time salaried and hourly workers, including those who work in its fulfillment centers and in customer service.

Until now, birth mothers were eligible for eight weeks of paid maternity leave, and there was no paid leave for other parents, putting Amazon well behind many technology companies' offerings, particularly recently. Within the past year, a growing number of companies have been offering generous extensions of paid leave, including Netflix, MicrosoftJohnson & Johnson and Vodafone. Silicon Valley companies like Facebook and Google have also long had generous benefits for working parents.

Amazon, however, is also adding another feature to its program that appears to be unique. Under its new "Leave Share" program, employees will be able to share all or a portion of the six-week parental leave with a spouse or partner who works at another company but doesn't have access to paid leave.

Say a woman who works at Amazon has a baby and wants her husband to have some time at home with the child, too, but he doesn't receive paid parental leave in his job. She could use all of her maternity leave and two weeks of the parental leave, and then come back to work and "share" the remaining four weeks with her spouse.

The pay for those four weeks that she did not take would then be added to her next paycheck, as long as her non-Amazon spouse affirmed that he does not receive paid parental leave benefits from his employer. Parental leave can also be shared between same-sex partners or adoptive parents.

"I’ve been doing this for 20-something years and I’ve never heard of anything like this," said Bruce Elliott, the manager of compensation and benefits for the Society for Human Resource Management. "Honestly this seems to be one of the most unusual twists to leave benefits I've ever seen," he said.

Another new feature, which Amazon is calling "Ramp Back" and is designed for birth mothers and primary caregivers, lets employees ease back into work over an eight-week period at a reduced schedule. In May, the editorial director of Working Mother Magazine said that 23 percent of the 100 companies on its list of the best workplaces for professional moms had an "automatic phase back" program that offered something similar.

Amazon did not make an executive immediately available to answer questions about the new policy. But in its memo, it said it began considering changes to its leave policy in early 2015, and examined the programs at other companies, conducted employee focus groups, and surveyed its new mothers and other workers.

"In developing these new policies, we focused on inventing features which create choice and flexibility, like the Leave Share and Ramp Back programs," the company wrote in the memo.

The announcement comes several months after a bruising article in the New York Times that depicted a hard-driving, 24/7 workplace culture, which sparked a war of words between the newspaper and Amazon.

Yet the move also comes at a time when many companies are not only adding more time off to their parental leave benefits, but getting more creative in the kind of benefits they offer new parents.

Vodafone said it would allow new mothers to return to work on a part-time basis for six weeks — while still receiving their full salary. Accenture is letting new parents opt out of traveling the first year after a child is born, basing them with local clients. The private equity firm KKR is paying for nannies and infants to travel with new parents during their first year of life. More and more employers are offering paid paternity leave — and encouraging fathers to take it.

Elliott said companies are likely making such updates to get ahead of potential regulatory changes, as paid family leave increasingly becomes a topic on the presidential campaign trail. Employers would also prefer to stand out on benefits rather than salary, he said, because there's much more flexibility in redesigning or even cutting benefits if needed over time, while doing the same to base pay is much harder.

Meanwhile, employers are also likely making such distinctive twists to differentiate themselves with millennial employees, who frequently see parenting as a joint responsibility and insist on flexibility. "They have not really started to multiply," Elliott said. "But when they do start to have families, this is the type of stuff they're going to demand."

Read also:

Like On Leadership? Follow us on Facebook and Twitter, and subscribe to our podcast on iTunes.