Following a national push for workplace policies that better support families, San Francisco just became America's first city to require businesses to offer new parents fully paid leave.

The measure, unanimously approved Tuesday by the city’s Board of Supervisors, will provide mothers and fathers six weeks of time off with sustained income a rare benefit in the United States, available most often to high-income workers and those in the technology sector. The help, expected to take effect in 2017, would also be available to parents who adopt.   

“The vast majority of workers in this country have little or no access to paid parental leave, and that needs to change,” Supervisor Scott Wiener, a proponent of the rule, said at a news conference.

Supporters say the action tackles income inequality, since the country’s low-wage workers are among the least likely to have access to any paid time off. The measure will undergo another formal vote by the board next week and is expected to be signed by Mayor Ed Lee.

While some parents have expressed relief,  small business owners have complained the city mandate will hurt their bottom lines. The measure would apply to companies with at least 20 workers.

“They don’t necessarily have the resources,” Dee Dee Workman, vice president of public policy at the San Francisco Chamber of Commerce, told the Associated Press. “They can’t absorb the increases in cost.”

Just three states today provide partially paid family leave. California, New Jersey and Rhode Island supply four to six weeks of the benefits, financed through disability insurance programs. 

Since California passed the nation’s first paid leave law in 2002, workers in the state have since filed at least 2 million claims, applying mostly for days to spend with newborns. The law boosted wages of mothers with young children, researchers have since found, and bolstered their ties to the workforce. 

New Jersey, meanwhile, added the benefit in 2009. Most employees who requested paid leave applied for time after childbirth, a Rutgers University Study found. New mothers who used the benefit, researchers saw, were far more likely to return to work and, eventually, earn higher pay.