Newly elected California Gov. Gavin Newsom (D) on Thursday proposed what would be the most generous paid parental leave policy in the nation: six months of partially paid leave so parents or other family members can care for a newborn or newly adopted baby.

Right now, some California parents have access to a combined four months of leave at partial pay. Those who get less include adoptive parents, same-sex couples and single parents.

Two-thirds of countries in the Organization for Economic Cooperation and Development guarantee six months of paid time off to new mothers. Newsom’s plan doesn’t go that far. Instead, the proposal, unveiled as part of his 2019 budget, would allow two caretakers to split six months off, according to a fact sheet provided by his office. One parent could take three months, and the other parent or partner or another family member could take three more months, or vice versa.

The policy would roll out slowly. At a press conference unveiling the state’s $209 billion budget on Thursday, Newsom said that leave would be paid for mainly with existing funds.

“It’s a developmental necessity,” Newsom said of paid leave. “We’re committed to this.”

Newsom’s proposal counts as groundbreaking and radical for the U.S., the only developed country in the world that doesn’t guarantee paid time off to new mothers; just two of 34 OECD countries do not guarantee paid leave to new fathers. And it comes at a time when Democratic state and local politicians around the country are proposing new liberal social programs ― beefing up Obamacare protections and provisions and passing greater labor protections. These guys are just catching up with others around the world, however.

“Look, the whole world has this, except for the United States,” said Ruth Milkman, a sociology professor at the Graduate Center of the City University of New York and a co-author of a book analyzing California’s leave policy. “This is not some utopian proposal. In the U.S. it would be a breakthrough.”

California’s policy would be a big step up from what the state currently offers: six weeks of caregiving leave, plus six to eight weeks for birth mothers through the state’s disability fund. The policy covers new parents and those who need time off to care for a sick loved one, offering a percentage of pay up to $1,216 a week.

It’s not clear if the extension would include caregiving leave; about 13 percent of Californians who seek paid leave need it to look after sick spouses, partners, children or parents, according to the state’s data.

New York, New Jersey and Rhode Island currently offer paid parental and caregiving leave, and Washington state, the District of Columbia and Massachusetts have policies set to start paying out within the next couple of years. These states offer between four and 12 weeks to new parents.

There’s a belief in the U.S., promoted mostly by business interests, that paid maternity leave is costly and hurts businesses. That’s a myth, said Milkman.

California’s existing program, started more than a decade ago, is relatively cheap. Workers in the state pay a 1 percent payroll tax on wages of up $115,000 to fund the program. And the fund is currently running a surplus, Newsom said Thursday. One way to pay for an expansion would be to tap into that surplus. He also mentioned raising the payroll tax as an option or raising the income limit so those earning more than the current taxable ceiling would contribute more.

It’s a small price to pay for the peace of mind in knowing that if they need time off for a health crisis or new child, they can take it, said Milkman.

“The money is not a lot, and it is so worth it,” she said.

And businesses have been largely unaffected by the paid leave program, according to a widely cited survey Milkman co-authored a few years ago. For those employers already offering leave, the policy means they spend less on the benefit.

There are some issues with California’s existing law: Job protections are limited. Many employers still have leeway to fire workers who take leave ― a limitation that activists hope Newsom will address.

Worryingly, even after more than a decade, many Californians don’t know they have access to paid leave. Take-up rates for leave have been low.

Newsom’s announcement could help raise awareness. “It can fuel the momentum we need to make this happen the way it needs to happen,” said Jenya Cassidy, an activist who helped pass the state’s first law. The director of the California Work & Family Coalition, she said the group hopes to work with the governor’s office to sharpen and improve the proposal.

The budget Newsom unveiled Thursday offered up a bunch of goodies for young children and their parents, including a plan for statewide universal pre-K and all-day kindergarten, as well as more money for subsidized child care. He also announced an increase in benefits to undocumented immigrants. It was an astonishing contrast to the policy priorities of the Trump administration.

This comes at a time when Democratic leaders in blue states are pushing progressive agendas that go far beyond what the divided federal government is capable of these days.

Just this week, New York Mayor Bill de Blasio proposed giving workers in the city two weeks of paid time off each year ― the nation’s first guaranteed vacation policy.

The egalitarian nature of Newsom’s scheme could avoid one of the pitfalls of paid leave: putting women at a disadvantage in the workplace. Mothers wind up taking long workforce leaves, and fathers don’t. Under his plan, if parents want their child to have six months of care provided by a family member, fathers would theoretically have to step up. Mothers still take the majority of leave in the state.

The effect of a paid leave policy on improving public health and the economy is hard to overstate.

Studies have shown that paid maternity leave reduces infant mortality rates, increases the amount of time women spend breastfeeding and makes it more likely that infants will be immunized.

Paid leave for women also helps keep them in the workforce. And the U.S. lags other nations when it comes to the percentage of women who work outside the home.