This story is part of our series on new California laws that take effect on Jan. 1, 2016.

California will have an expanded Equal Pay law beginning in January.

A new law taking effect prohibits employers for paying men and women differently for "substantially similar work." The existing law only specifies pay must be the same for "equal work" - a definition courts have interpreted narrowly. 

UC Davis Professor of Law Emerita Martha West says the law also prohibits employers from retaliating against employees who discuss their salaries

"So the important part is that women need to find out what men are making in the work place," she says."Women need to start talking to each other and talking to their colleagues at work to find out what everybody is making."

But West notes the new law may not help all women. 

"You have to have a man in the same work environment doing substantially similar work," he says. "So a lot of work environments are still single sex. And this law will not help women who are in low paid jobs where there are no men doing those jobs." 

West says it will take several court cases to see how the law’s "substantially similar" language is interpreted.