– When Elvira Lopez's son Javier was born in March 2016, the Amazon.com warehouse employee took advantage of a perk that few U.S. hourly workers enjoy: She took 20 weeks of paid maternity leave, and after that, a six-week gradual ramp-up back to work.

"I was able to go to appointments. You know how hard that can be," said the 28-year-old Lopez, who lives in Phoenix. The time off also gave her the opportunity to spend time with her older daughter, 11, during the summer and to visit California, where she's from. "We went to Disneyland. Twice."

Lopez is one of 11,000 U.S. employees to have enjoyed Amazon's overhaul of parental-leave benefits in November 2015. About 72 percent of them are, like Lopez, operations and logistics workers paid by the hour and on the lower end of the salary scale, according to data released for the first time by the company.

Amazon's move to revamp its parental-leave benefits coincided with a wider wave of perk enhancements among booming U.S. technology companies concerned about retaining talented employees, especially women, who are underrepresented in tech. Microsoft and Netflix had announced major improvements to their parental-leave policies earlier that year.

It also came at a time when the fast-growing company started making its way to the top of the list of major employers among the Fortune 500, mostly due to furious hiring at its warehouses.

Amazon currently employs 382,400 around the world, and if the company completes its takeover of Whole Foods, it could become the second-biggest employer on the list after Walmart.

What's interesting about Amazon's policy, though, is that the Seattle e-commerce giant extended to its burgeoning army of relatively low-paid warehouse workers the same enhanced benefits that its highly paid software developers and executives get.

That gives the majority of Amazon's U.S. workforce access to generous leave policies that are rare beyond the upper echelons of American workers or among those living in the few states with paid leave laws. (Washington state's paid family-leave law takes effect in 2020.)

According to a report by the Bureau of Labor Statistics last November, close to a quarter of private-industry workers in management and professional occupations had access to paid family leave. In contrast, only 7 percent of people in service occupations, and 6 percent of workers in transportation and production activities had the same benefit.

"Privately offered paid leave has grown most in sectors that recruit from a small group of highly skilled workers," wrote the authors of a Brookings Institution paper published in May. That inequality can be seen even within large companies that employ people at both ends of the skill spectrum.

When Starbucks earlier this year said it would expand its parental benefits starting in October, it gave nonstore employees a much better deal than it did baristas. Walmart, Amazon's archrival and America's largest private employer, also has a two-tier system.

Parental benefits are available to Amazon employees who work more than 26 hours per week. To moms who give birth, Amazon offers 20 weeks of paid leave. Four of those weeks can be taken before the baby comes. Six of those weeks can be shared with their partner.