Governor Jerry Brown signed the landmark California Fair Pay Act on Tuesday – described as the strongest equal pay protection for women in the nation.

The law provides that women in the state should receive equal pay for doing “substantially similar work” as their male counterparts, and have the right to compare salaries with co-workers without fear of retaliation from employers.

“I don’t think this is going to solve all of our problems but I think this is definitely monumental,” said assembly member Cristina Garcia, co-author of the bill, SB 358, and vice-chair of the California Legislative Women’s Caucus. “We’ve had a law on the books for six decades and while we’ve seen some progress, we can’t wait another 40 years to get to equality, so I’m excited to have something new to help accelerate that progress.”

The Fair Pay Act changes the rules surrounding equal pay from a standard of “equal work” to one of “substantially similar” work, closing what legislators described as a loophole that made it difficult for women to prove pay discrimination.

“Equal can really be a technical term, so courts can get really hung up on making sure two workers are in the exact same position,” said Mariko Yoshihara, legislative counsel and policy director for California Employment Lawyers Association, one of the sponsors of the bill.

Senator Hannah-Beth Jackson, co-author of the bill and Chair of the Women’s Caucus, said that duties don’t need to be identical to deserve equal pay, and that women bring distinct and useful skills to the workplace that should hold equal value to the skills men bring to the same position.

“We really need to change the way we look at jobs through a gender lens,” she said.

Considerations such as seniority and merit are still allowable grounds for pay differences under the act, but an employer must now prove that “differences in wages are due to factors other than gender and that these factors are not arbitrary but are directly related to the job duties”, said Jackson during a press conference after the bill’s passage.

Jackson also said that the parameters for what constitutes pay discrimination are broadened under the legislation to include jobs at different worksites of an employer, or jobs under different titles but with substantially the same duties.

“It will mean, for instance, that the female housekeepers that clean rooms in a hotel could legally challenge the higher wages paid to their male janitor counterparts who clean the lobby,” she said.

Across the United States, women make on average 78% of what male counterparts make. California women fare better, bringing home on average 84% of men’s pay, according to a 2014 report from the American Association of University Women, but the gap increases for women of color and mothers.

“African American women average 64 cents for the dollar every man makes and Latinas get 44 cents for every dollar a man makes here in California” said Jackson, pointing out many of these women represented low-wage workers who were also single mothers.

That translates to the average male worker in California bringing home median pay of $50,268 compared with $42,199 for women, a difference that takes $33bn out of women’s pockets each year in the state, according to Jackson.

The disparity jumps dramatically in certain places, like the technology hub of Silicon Valley, where men with graduate or professional degrees earned 40-73% more than equally educated females in 2012, according to the Silicon Valley Index, an annual economic snapshot of the region. That was a decline from a shocking 97% disparity in pay in 2010. That inequality was highlighted earlier this year, after venture capitalist Ellen Pao lost a three-year fight with her former employer, Kleiner Perkins, centering on gender issues.

The law also addresses the difficulties women face in even discovering pay discrepancies, by making it illegal to retaliate against employees who talk about their pay at work.

While all US workers have the right to discuss their salaries in practice it is taboo, with many companies having distinct policies and punishments for those who share such information.

“Everyone talks about ‘you should have asked for more’, but if you don’t know what other people are making, you don’t know what to ask, where the bar is at,” said Garcia.

The Fair Pay Act is part of a package of far-reaching economic bills aimed at women that were introduced in this legislative session. Along with equal pay, those bills focused on childcare, making workplaces more family-friendly and eradicating poverty. Two other key bills in that package are still working their way through the final days of voting.

AB 1354 would enforce recent federal contractor standards on state contractors as well, requiring them to submit compensation data based on sex and race to regulators.

AB 1017 would prohibit employers from asking new hires for past salary information. Critics of that practice say that it puts women at an unfair advantage by saddling them with lower wages from one employer to the next, basing future compensation on past salary rather than on existing company scales.