Tennis star Serena Williams is the highest paid female athlete in the world and she’s using her prominence to try and help close the gender pay gap for black women.

Black women earn 67 cents for every dollar white men earn, Williams said in an impassioned essay in Fortune. She’s calling for dedicated action, legislation, employer recognition, and courage for employees to demand more.

Williams has dominated tennis for 15 years. In 2002 at age 20, she was the top-ranked player in the world. In May at age 35, she was the oldest woman ever to hold the No. 1 spot. She’s won 86 percent of her matches, with a record 23 Grand Slam singles titles. Her career prize money of $84 million is more than twice as much as any other female athlete’s, Forbes reported.

Williams spelled out how black women lag behind men and white women for pay:

Black women are 37 cents behind men in the pay gap—in other words, for every dollar a man makes, black women make 63 cents.
I’d like to acknowledge the many realities black women face every day. To recognize that women of color have to work—on average—eight months longer to earn the same as their male counterparts do in one year. To bring attention to the fact that black women earn 17 percent less than their white female counterparts and that black women are paid 63 percent of the dollar men are paid. Even black women who have earned graduate degrees get paid less at every level. This is as true in inner cities as it is in Silicon Valley.
Together, we will change the story—but we are going to have to fight for every penny.

Williams made her first foray into Silicon Valley in May when she joined the board of SurveyMonkey, an online survey startup that gathers customer feedback from online surveys and is used by most Fortune 500 companies, according to Fortune.

Silicon Valley has a poor track record with women and diversity:

Survey data depends on the types of questions asked and knowing what to ask, TechCrunch reported. That unique insight can be hard to get in a room full of the same types of people.

Williams brought a much-needed voice to help shape SurveyMonkey’s future, CEO Zander Lurie said. Williams’ “voice on the board sends a strong message to our company, investors, and the industry,” he said.  “We want change agents at our table.”

Williams told TechCrunch she is driven to ask what’s happening, and why, and is fiercely committed “to letting all voices be heard.”

Eight of the top 10 highest-paid female athletes are tennis players, according to Forbes:

It is the one major sport where, when comparing men and women, the money is in the same stratosphere.

On July 31 — Black Women’s Equal Pay Day — William said she is in a rare position to be financially successful beyond her imagination:

“I had talent, I worked like crazy and I was lucky enough to break through. But today isn’t about me. It’s about the other 24 million black women in America. If I never picked up a tennis racket, I would be one of them; that is never lost on me,” she said in her Fortune essay.

Most black women don’t have the same support that she had, Williams said. They often don’t speak out about what is fair and appropriate in the workplace, and when they do, they are often punished for it.

“It is my hope that I can give a voice to those who aren’t heard in Silicon Valley, and the workforce as a whole,” Williams said.

She urged Black women to be fearless and speak out for equal pay. “You have to believe in yourself when no one else does,” she said. “Let’s get back those 37 cents.”

Williams and fiancé Alexis Ohanian, founder of Reddit, are expecting their first child.