The state Senate has given unanimous support to a bill that was born from the inequities adoptive parents can face in the workplace.

Combining proposals by Sens. Brian A. Joyce, D-Milton, and Mark C.W. Montigny, D-New Bedford, the bill would give adoptive parents the same parental leave rights as birth mothers.

The double standard that exists in some companies' leave policies is "completely unfair, particularly in a society where we are saying, 'We want to encourage adoption' ... yet we offer very little by way of service," said Montigny, who pointed to pro-adoption messages everywhere from the teen pregnancy issue to both sides of the abortion debate.

The federal, gender-neutral Family and Medical Leave Act requires, among other provisions, that companies with at least 50 employees give workers up to 12 weeks of unpaid leave to care for newborn, adopted or foster children. By extending to companies with as few as six employees — and similarly including adoptive and birth mothers — the Massachusetts Maternity Leave Act's allowance of up to eight weeks unpaid leave is in some ways more comprehensive.

But this comes with one major limitation: It applies only to women.

That's what Joyce set out to change when he filed a bill that would make the state maternity leave act gender-blind.

"The bill is reasonable and allows equal opportunity for all men and women," he said, describing how the impetus came from a friend in a same-sex marriage. While the man's employer gave him leave to care for his adopted baby, he realized he wasn't entitled to this time off under state law.

"He pointed out, quite correctly, that the law should be gender-neutral because we have stay-at-home dads who may be the primary caretaker," said Joyce, who pointed to a quirk under the current statute. Adoptive mothers in a same-sex marriage are both entitled to unpaid leave, while adoptive fathers are left in the cold.

Montigny's provision pushes equity even further by requiring that when a company offers any leave benefits — including those above state and federal minimums — they must be identical for adoptive parents and birth mothers alike.

Locally, the push came from Judith Lima, a Dartmouth mother who adopted her children from South Korea, with her husband John, in 2000 and 2005.

"There are some companies who embrace adoption and extend a maternity leave to the moms who adopt children, and there are companies that do not see adoption as motherhood," she said.

"A mother is someone that loves a child, teaches a child, protects a child," Lima said. "Whether you give birth or whether you adopt a child, you're still a mother. ... I would hope that for the companies that don't see motherhood holistically like that, I want to believe that it's an oversight."

Lima described the extension of leave rights to adoptive parents as a no-brainer.

"The bonding piece is a critical piece for any child," she explained. "And unfortunately, for adoptive parents, we have it that much harder because it's very rare that you adopt a child and get them early, early on."

Although Lima said her daughter Hannah seemed to take to her immediately, 11-month-old Colby took a bit longer.

After being shuttled between people and continents, "everything about what was comfort to him (was) now gone. ... And we (had) to fill that gap," Lima said.

The parental leave rights bill now heads to the state's House of Representatives, and Lima said she is optimistic it will ultimately become law.

"I can't imagine that anybody would ever object to such a thing," she said.

Sen. Marc R. Pacheco, D-Taunton, certainly doesn't.

"It's about equity and fairness and it's also about children," he said, stressing that, if anything, society needs more people who are willing to adopt. And since these parents can save the state resources, Pacheco said, supporting them "also makes financial sense."

Montigny predicted the bill would be bolstered because debates over issues like same-sex marriage and unpaid leave in Massachusetts have already been won. Still, he did acknowledge the potential for some resistance from the private sector.

The Boston-based Retailers Association of Massachusetts had yet to take a firm position as of Wednesday, according to President Jon B. Hurst, who nevertheless said the bill could see significant support as a step toward greater equality.

"As long as it's flexible enough that you aren't requiring new costs — new paid benefits and leave — it may lessen any level of objections from the business community," he said.

However, he wondered whether the requirement of equal-benefits-for-all might lead some businesses that offer enhanced leave benefits to scale them back.

In the meantime, Montigny said, "There'll be some people out there that will squawk. And my feeling is, 'Let them.' Sometimes you just have to do the right thing."