For example, the study found that people who make more than $75,000 annually are twice as likely to receive a paid leave benefit than those who make less than $30,000 a year. In addition, the study found 1 in 4 new mothers in the U.S. are back at work just 10 days after childbirth.

Related: AmEx unveils big weapon in the parental leave arms race

“The U.S. is one of the only countries in the world without a national paid family leave program, so people are largely at the mercy of their employer for this vital benefit,” Cotter says. “Research shows that the lack of access to paid family leave has a powerful negative impact on family health and financial stability.”

Lawmakers -- starting to pay attention?

The issue of paid family leave has largely flown under the radar in recent years, with some communities and states passing laws to expand the benefit. Nothing like a bipartisan consensus has emerged, but the 2016 campaign saw both major party presidential candidates talking about some form of paid family leave.

Over the last week, several media outlets have reported President Trump will make good on a campaign promise and offer a national policy for paid family leave. The plan would give mothers and fathers six weeks of paid leave after the birth or adoption of a child, to be paid for through the unemployment insurance system.

Traditionally, Republicans have opposed a mandated approach to this issue, so the response on Capitol Hill remains to be seen. For her part, Cotter says the Trump plan is inadequate.

“Trump’s new proposal — six weeks partially paid for new babies only — is a far cry from the solution we need,” she says.

Different rules for different workers

The PL+US study outlines how corporate America has approached the issue of paid family leave. It finds such benefits are often limited to employees in corporate headquarters.

Starbucks, for example, provides 18 weeks of fully paid leave for new mothers and 12 weeks of fully paid leave for fathers in corporate headquarters, but only six weeks for birth moms who are in-store employees, and no time off for dads or adoptive parents in that category.

Likewise, Walmart, the nation’s largest employer, provides 12 weeks of paid leave for birth mothers who are corporate employees, but give only partial pay for six to eight weeks for birth moms who are hourly employees — if they work full time. Walmart has 1.2 million hourly-wage employees in the U.S.

The study includes a list of 36 large employers, many of whom have different policies in place for corporate workers, as opposed to hourly-wage workers. In addition, few employers offer equitable policies for dads or adoptive parents.

The study finds another issue: outsourcing work to subcontractors.

“We further found evidence that the outsourcing of work to low-wage, low-margin subcontractors by many large employers furthers the schism between those who have access to paid family leave and those who do not,” the report says.

A role for HR leaders?

Some have speculated that the demand from workers for paid family leave policies will result in many more employers expanding benefits in that area — even if legislation becomes gridlocked.

However, the Society of Human Resource Management (SHRM), says in a white paper earlier this year that as a whole, change is not likely to happen overnight. “Despite widespread public interest — particularly from younger workers in the millennial generation — in evolving leave models to support caregiving, only 17 percent of employers offered paid parental leave in 2016,” SHRM says, drawing from an earlier study.

Alionna Gardner, an HR generalist/consultant with Kiwi Partners Inc., an HR consulting firm in New York City, says the U.S. has a long way to go to catch up with the norms of European countries, which have had generous family leave policies for years.

SHRM’s paper suggests that HR departments may be key players in the evolution of this benefit.

“[HR professionals] not only can encourage their companies to consider offering paid leave, but also can work to create cultures that embrace caregiving,” the report said. “After all, it ultimately makes no difference whether a company offers time off if employees are too scared to use it.”

“HR has to be the leader in the evolution of parental leave in America,” Gardner says in the SHRM report.

“We are the glue that holds businesses together and, more importantly, the catalyst that invokes change in policy and organizational development. Offering paid leave is a strategic move that allows businesses to become increasingly competitive.”