Xceed Financial has $942 million in assets and 58,000 members.

Freeborn estimated that 75% of the state's credit union workforce is female. That's approximately 14,500 women, based on 2014 data from the Bureau of Labor Statistics.

Under the law, employers must prove their wage differentials are based on a seniority system, a merit system, a system that measures earnings by quantity or quality of production, or a bona fide factor other than sex, such as education, training or experience. It also forbids employers from retaliating against employees who disclose their wages.

There is one sizeable unknown, however, according to California-based employment attorneys Yves Nguyen and Roland Juarez of the Hunton & Williams law firm.

"SB 358 does not define what 'substantially similar work' means," they wrote in an analysis. "As a result, it is unclear whether employees with different job titles, but who perform many similar duties, may be entitled to receive the same wages. In addition, the bill eliminates the requirement that comparable employees be in the same establishment, which means an employee working in one office location for the employer could also challenge the wages paid to a male counterpart holding the same position at a different office location."

That could mean wages in relatively expensive parts of the state could become a factor throughout the state.

"What you get paid in the Bay Area is a whole lot more than you get paid when you're here in the Inland Empire, where the league is located, because the cost of housing is significantly less," Diana Dykstra, president/CEO of the California and Nevada Credit Union Leagues, noted. "The competition for jobs is significantly less."

The law could also limit managerial discretion over salary offers and raises, though most credit unions already use wage bands, Dykstra said.

"So if you do this job, this is your wage band. The difference between the top and the bottom is not huge. The issue really becomes can they pass the test of seniority, education and experience. That's the subjective," she said. "If I have a masters degree from the University of Phoenix, and somebody else has a masters degree from MIT, are they different?"

The new law also provides a private right of action to sue employers. Employees who win could receive lost wages plus interest and damages. The state could also prosecute.

Freeborn, however, didn't believe the law creates a competitive disadvantage for California credit unions.

"That's the sort of charge that's always leveled by people who oppose government action to help right a wrong situation," she said. "They said the same thing about the first equal pay laws and about family leave when it was first introduced."

She added, "As I've mentioned many times while discussing these issues, I don't think there are many credit unions that intentionally discriminate against women – either in pay or leadership decisions – but these improvements in the Fair Pay Act will cause all credit unions to examine their practices and policies and make sure they're doing right by their women employees."

Dykstra, who said she spent 29 years inside credit unions, agreed.

"I never felt like there was injustice," she said. "There may have been and I just didn't know it."