San Francisco approved a measure Tuesday making it the first place in the nation to require businesses to provide fully paid leave for new parents.

Advocates say the issue is gaining momentum across the country much like the debate over a higher minimum wage.

The San Francisco Board of Supervisors voted unanimously in favor of the measure after supporters said six weeks of fully paid leave is needed because too many families can't afford to take time off after a child is born or adopted.

Small business owners countered that it's the latest in a long list of city mandates— including paid sickleave and health coverage— that unfairly targets them.

The U.S. lags other countries in providing parental leave.

Federal law grants workers up to 12 weeks of unpaid leave. California, Rhode Island and New Jersey provide partial pay, with the money coming from employees. Legislators in New York last monthapproved up to 12 weeks of partial pay.

The state of California currently allows workers to receive 55 percent of their pay for up to six weeks to bond with a new child. The money comes from a state insurance program funded by workers.

The San Francisco measure requires employers with at least 20 employees to make up the rest.

Some private employers such as Netflix are generous with leave as a way to retain workers, and people who work for the city and county of San Francisco are entitled to 12 weeks of full pay.

Supervisor Scott Wiener, who pushed for paid leave, has said the benefit is another step toward addressing income inequality, much like the $15 hourly minimum wage legislation that California Gov. Jerry Brown signed Monday and San Francisco approved for workers in 2014.

"The vast majority of workers in this country have little or no access to paid parental leave, and that needs to change," he said at a news conference before Tuesday's vote.

Among the dozen or so attendees was Kim Turner, a nonprofit attorney who took advantage of the state parental leave program. She says full paid leave would have been better.

"I do think employers should be pitching in more," she said. "I think we all need more help. It's just so hard to make ends meet with little ones in the house."

A group representing small businesses disagreed.

"They don't necessarily have the resources, they can't absorb the increases in cost, and they feel like it's kind of relentless, it's one thing after the next," said Dee Dee Workman, vice president of public policy at the San Francisco Chamber of Commerce.

Businesses with at least 50 employees must comply starting in January 2017. Businesses with at least 20 employees have until January 2018 to comply.