American tennis star Serena Williams is speaking out and the world is listening.

Serena decried that they (black women) would have to work on average eight months longer to earn the same as male counterparts in one year.

"Black women are the cornerstone of our communities, they are phenomenal, and they deserve equal pay," Williams tweeted Monday with a picture of herself wearing a T-shirt saying "Phenomenal Woman."

"For every dollar made by a man, black women make 63 cents in the United States.

"Black women earn 17 percent less than white women, and black women with graduate degrees get paid less at every level, wrote Williams.

The 23-time Grand Slam singles champion quoted data showing that only 44 percent of white men recognize the pay gap as an issue.

"I have been treated unfairly, I've been disrespected by my male colleagues and -- in the most painful times -- I've been the subject of racist remarks on and off the tennis court," wrote the 35-year-old.

"The cycles of poverty, discrimination, and sexism are much, much harder to break than the record for Grand Slam titles," she added, calling for legislation and action to change the status quo.

Williams, who announced her engagement to Reddit co-founder Alexis Ohanian last December, is pregnant with her first child. She plans to return to competitive tennis next year.

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