How long do black women have to work to earn as much as white men?

And Monday, July 31, known as Black Women's Equal Pay Day, is the date into 2017 that black women had to work to catch up to what their white male counterparts earned in 2016 alone.

Twitter users, including several notable leaders and celebrities, took to the social media platform Monday to address the wide wage gap:

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According to the Bureau of Labor Statistics, women in the United States working full-time and salaried jobs in 2016 earned approximately 20 percent less than what men in the same positions earned.

But that disparity is even worse for black women, who earn 17 percent less than their white female counterparts.

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Statistics show black women in particular are paid approximately 63 cents on the dollar compared to white, non-Hispanic men.

In a Fortune Magazine essay penned by professional tennis player Serena Williams on Monday, Williams calls on her fellow black women to reclaim those 37 cents.

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“The issue isn’t just that black women hold lower-paying jobs. They earn less even in fields of technology, finance, entertainment, law, and medicine.” she wrote. “Changing the status quo will take dedicated action, legislation, employer recognition, and courage for employees to demand more. In short, it’s going to take all of us. Men, women, of all colors, races and creeds to realize this is an injustice. And an injustice to one is an injustice to all.”

Williams also included surprising findings from a SurveyMonkey poll, including that 69 percent of black women perceive a pay gap, while only 44 percent of white men recognize there’s a pay-gap issue.

“Black women: Be fearless. Speak out for equal pay. Every time you do, you’re making it a little easier for a woman behind you. Most of all, know that you’re worth it. It can take a long time to realize that. It took me a long time to realize it. But we are all worth it. I’ve long said, ‘You have to believe in yourself when no one else does,’ she wrote. “Let’s get back those 37 cents.”

Read Williams' full essay at Fortune.com.

Facebook COO Sheryl Sandberg and her global Lean In organization, which focuses on "empowering women to achieve their ambitions," have also teamed up with small businesses in Richmond, Virginia; Indianapolis, Indiana; and Atlanta to offer 37 percent discounts to represent the pay gap for black women.