What do Papua New Guinea and the United States have in common? Logistically, geographically, and politically not much, but they are the last two of 185 surveyed nations to not mandate paid parental leave, according to the International Labor Organization. Although that may soon be changing one US city at a time….

On Tuesday, San Francisco adopted a new measure that will require businesses to provide six weeks of fully paid leave for new mothers and fathers. The legislature is the first of its kind for any city, or place, in the US.

"The vast majority of workers in this country have little or no access to paid parental leave, and that needs to change," city supervisor Scott Wiener said at a news conference.

But can San Francisco's new policy be replicated elsewhere? Not likely. San Francisco benefits from a set of unique circumstances that make a city-mandated parental leave program possible, but its situation is far from average for US cities.

For one, San Francisco's paid parental leave had a solid foundation from an already established partially paid family leave program mandated by California at the state level. The program provides new parents in California six weeks of leave with 55 percent of their income paid by a public disability fund. It is one of only a handful of similar state programs.

The preexisting paid parental leave program also helps San Francisco employers. Employers are only required to cover the remaining 45 percent of new parents' income, according to Fortune.

The mandate will only affect businesses that have a minimum of 50 employers this year; to prevent the mandate from overburdening smaller companies, businesses with 35 or more employees must comply by July 2017, and companies with 20 or more employees must be compliant by January 2018.

Despite the minimum employee limit, policymakers have warned that the plan could have an impact on business. "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."

In addition to logistics, San Francisco is home to a number of private companies where progressive family policies are already broadly practiced. Adobe, Apple, Facebook, Google, Netflix, Pinterest, Reddit, Twitter, and Yahoo! are all major companies with premium parental leave programs that are located in or around San Francisco.

But the new program has also drawn sharp criticism. In a statement released Wednesday, the Independent Women's Forum managing director Carrie Lukas called the plan "anathema to true flexibility."

"If we want workers to have the compensation packages that they want – including higher wages and better benefits – then policymakers should focus on facilitating job creation so that workers have a variety of employment opportunities and bosses have to compete to keep them. Unfortunately, this type of employment mandate takes us in the opposite direction and will be another barrier to job creation."

In San Francisco, the new mandate will take effect for businesses with 50 or more employees in January 2017.

New parents will be eligible for the fully paid leave if they spend 40 percent or more of their work week in the city, according to the AP.