Massachusetts has leapfrogged over all other states to pass the most robust equal pay law in the country.

The law takes a step that is completely unique: it prohibits employers from asking prospective hires about their salary histories until after they make a job offer that includes compensation, unless the applicants voluntarily disclose the information. No other state has such a ban in place.

Many employers require applicants to give them a salary history at the outset or during the initial steps of the hiring process, usually to determine how much they should be paid and whether the employer can afford their salary. But this disadvantages women, who, thanks to a variety of factors that can include outright discrimination, make less than men on average. Women make less than men in their first jobs even when education and field are taken into consideration, and they are also penalized in salary negotiations, while men get an advantage. If the next employer bases a salary on the previous one a woman was earning, that discrimination will only be furthered.

Massachusetts’s new law also mandates that employers pay men and women the same not just when they do the exact same work, but when their work is “comparable.” Most laws only require men and women in the exact same job to be paid equally. The state defines comparable work as being “substantially similar” in skill, effort, responsibility, and working conditions — not just based on job titles or descriptions. It does, however, allow for differing pay scales based on seniority — so long as a lack of seniority for a female employee isn’t related to pregnancy or family leave — merit, production, geography, education, experience, or training.

Women’s work has long been undervalued even when it’s substantially similar to what men do.Housekeepers make less than janitors, for instance. And when women move into higher-paying, male-dominated jobs, the pay drops.

There was a movement in the 1970s and 80s among state governments to ensure comparable pay equity in their own workforces. They ended up spending $527 million to adjust women’s pay to make it equal with men who had essentially the same job duties, eliminating about 20 percent of women’s wage gap.

A paper at the time found that a national pay equity law, one that looks like Massachusetts’s, would eliminate more than a quarter of the overall gender wage gap.

The new law also bans salary secrecy, blocking employers from keeping their employees from talking about pay with each other. About half of all employees say they are either prohibited or discouraged from discussing compensation, even though they have a legal right to do so. That makes it incredibly difficult for women or other marginalized groups to discover whether they’re being unfairly paid less than their colleagues.

A handful of other states have passed their own equal pay laws aimed at closing the gender wage gap. California passed one at the end of last year mandating pay equity for comparable work and banning salary secrecy, and New York passed a package of bills that included prohibiting salary secrecy. But none of them have gone as far as Massachusetts in including a ban on employers asking for salary histories.

Massachusetts’s new law unanimously passed the state legislature, and Gov. Charlie Baker (R) has said he will sign it into law.

Meanwhile, progress toward passing national legislation to address the gender wage gap has been blocked in Congress. Republicans have repeatedly blocked the Paycheck Fairness Act, which would ban salary secrecy, and the Fair Pay Act, which would mandate equal pay for comparable work, never even gets a vote.

This post originally appeared at ThinkProgress.org on August 1, 2016. Reprinted with permission.

Bryce Covert  is the Economic Policy Editor for ThinkProgress. Her writing has appeared in the New York Times, The New York Daily News, New York Magazine, Slate, The New Republic, and others. She has appeared on ABC, CBS, MSNBC, and other outlets.