The San Francisco Board of Supervisors unanimously voted on Tuesday to prohibit employers from asking job applicants for their salary histories, a move several progressive cities and states have made in recent years in an effort to narrow the gender wage gap. Mayor Ed Lee signed the legislation into law on Wednesday, but it won’t take effect until 2018.
The legislation will also prevent an applicant’s current or previous employers from releasing her salary information without her consent. Advocates say that the salary-history question keeps women and people of color in a cycle of low pay, where one boss who pays white men more than their peers—or one bout of poor negotiation—can diminish a worker’s earnings for the rest of her career.
Mark Farrell, the supervisor who proposed the legislation, told Fortune that the idea appealed to him as a way to make “an immediate impact” on wage inequality by changing the behavior of the supervisors who make salary decisions. Other equal-pay legislation, like the Equal Pay Act of 1963, has proven easier for companies to wiggle around by keeping employees’ salaries confidential and arguing that almost any conceivable reason but gender justifies pay gaps between male and female employees. Farrell has noted that the national gender wage gap has only narrowed by a half cent each year since that act was passed, and if it continued at that rate, women and men won’t make the same salaries until 2059.
That’s a grossly misleading calculation, of course: Women’s work in the ‘60s was largely confined to domestic and service-industry positions, and women’s advancement into positions of leadership in every industry in the past couple of decades has contributed to as much of the wage gap’s closure as the general decline in wage discrimination. But Farrell’s point about the potential immediate benefits of the law is a good one. In the best-case scenario, prohibiting salary-history questions would stop unequal pay before it starts, or at least give employees a way out of underpayment with each new job.
Opponents of such laws, which currently exist in Philadelphia, New York, California, and Massachusetts, say that employers will still be able to introduce discrimination or unconscious bias into salary decisions by assuming that women and people of color are getting paid less at their current jobs and giving them lower starting offers anyway. Advocates argue that applicants can still voluntarily offer their previous salaries if they think it will help them in a negotiation. In an editorial published earlier this year, Bloomberg called a ban on salary-history questions a “gag rule” that hasn’t yet been proven to work as intended.
It’s true that these laws aren’t proven vanquishers of gender and race wage gaps, and there’s a simple reason why: They’re brand new. The first salary-history question ban took effect in California in January; Philadelphia’s was supposed to take effect in May, but it’s on hold while the city’s Chamber of Commerce challenges it in court for allegedly infringing on businesses’ rights to free speech. There is no data on these laws yet because they’ve barely begun to exist. Policymakers and advocates will need at least a few years of data to analyze before making a judgment on the impacts of this kind of legislation.
Still, there is a wealth of research on the gender wage gap, the psychology of negotiations, the trajectories of women’s careers, and the difference in starting salaries offered to men and women for the same jobs at the same companies. The thrust of that research points to a simple conclusion: Tying an employee’s pay to her previous salary will forever exacerbate a gender wage gap that exists even in the first jobs women and men take after college, even when controlling for major, occupation, location, and hours worked. The more cities and states that pass these laws, the better and more diverse data experts will have to help them quantify the impact of this worthy experiment a few years down the line.