San Francisco legislators have unanimously passed a law guaranteeing six weeks of fully paid maternity or paternity leave. The law makes it the first U.S. city to guarantee fully paid time off for new parents, and follows a similar recent decision by the state of New York that signals a growing shift in parental leave policies.

California law already requires that workers receive six weeks of leave for 55% of their pay – money that is financed by the state’s disability insurance. Under San Francisco’s new law, employers will cover the 45% difference.

Full- and part-time employees who work at least eight hours a week and spend at least 40% of the work week in the city’s boundaries will be eligible for the benefit. Businesses that employ 50 or more workers will begin offering fully paid leave beginning next January. Businesses with 35 to 49 workers will pay for leave beginning in July 2017, while businesses with 20 to 34 workers must comply beginning in January 2018. Small businesses with less than 20 employees will not be mandated to fully cover parental leave.

“Our country’s parental leave policies are woefully behind the rest of the world, and today San Francisco has taken the lead in pushing for better family leave policies for our workers,” said Supervisor Scott Weiner, the bill’s author, in a statement. “We shouldn’t be forcing new mothers and fathers to choose between spending precious bonding time with their children and putting food on the table.”

Weiner added that the bill is designed to help low-wage workers who cannot afford to take time off when having a baby. New parents must have been with the business for 180 days to be eligible, and have to stay 90 days after returning or repay the money.

“I am supportive of a cohesive philosophy of life-work alignment," says Jeff Scult, co-founder and president of San Francisco-based supplier Golden Goods. "Companies just need to build into their HR model, and while it will have an impact, the hope is that the human impact will outweigh all other – the employee returning feeling supported and life energized.”

The San Francisco Chamber of Commerce told USA Today it was taking a neutral stance on the issue, supporting extended parental leave but worried about the potential cost to businesses. Other San Francisco business associations opposed the law, with one calling it “unfair.” A study by the city’s Office of Economic Analysis said the law could cost San Francisco businesses up to $32.3 million annually.

Currently, only four states in the U.S. guarantee partially paid family leave for new parents. New York became the latest last week by passing a bill that covers 12 weeks paid time off for men and women and both part-time and full-time employees. California and New Jersey employees are guaranteed six weeks of paid time off while Rhode Island residents are eligible for four.

The New York program will go into effect starting in 2018. Employees will have 70 cents deducted per week (and eventually $1.40) that will be put into an insurance fund to pay for the leave.

Last year, President Barack Obama signed an executive order to allow federal workers six weeks of paid parental leave. The United States is one of only two nations that does not have a national paid leave law.