As the U.S. Open kicked off, the former First Lady spoke to the crowd at New York’s Arthur Ashe Stadium, where a special event was held to honor tennis icon Billie Jean King.

The occasion also marked 50 years of equal pay for male and female players in the tournament.

In 1972, King told tournament organizers she and her female colleagues would not return the following year unless they were paid equally. She had been awarded $10,000 for winning the women’s singles title, while men’s champion Ilie Nastase took home a $25,000 prize.

King—who won 39 Grand Slam titles throughout her career—went on to form the Women’s Tennis Association (WTA) and, thanks to a grant from a sponsor, helped bring about change that saw male and female players awarded the same winnings at the U.S. Open from 1973 onwards.

“Fifty years ago, everything was hanging in the balance. Billie Jean had a choice. She could put her head down, keep winning tournament after tournament, and just accept whatever check she was given.

“Or she could dig deep and break serve. She could make a stand,” Obama said at Monday’s event. “If you know Billie Jean, you know what she chose…and thankfully, the U.S. Open had the guts to listen.”

Today I was honored to celebrate @BillieJeanKing and the 50th anniversary of equal prize money at the @USOpen. Billie Jean didn’t just change tennis — she changed the future on and off the court for women and girls in the decades since. pic.twitter.com/w1BtovAWpu

— Michelle Obama (@MichelleObama) August 29, 2023

At this year’s tournament, U.S. Open singles champions will win a record $3 million each.

However, Obama argued Monday that the progress made by King and other activists was at risk of being undermined.

“Let us all summon a fraction of the courage and tenacity of women like Billie Jean King and continue to fight for a better, more just, more equitable future for all of our children,” she said. “We can sit by silently and hope that someone else will fight our battles. Or we can make our own stand. We can use whatever platforms we have to speak out and fight to protect the progress we’ve made and level the playing field for our daughters and their daughters.”

The bestselling author, philanthropist, and mom of two daughters said that, ultimately, female athletes’ battle for equal pay was about more than sports.

“Let us remember that all of this is far bigger than a champion’s paycheck,” she said. “This is about how women are seen and valued in this world. Sadly, we have seen how quickly progress like this can be taken away if we are not mindful and vigilant, if we do not keep remembering, advocating, organizing, speaking out and, yes, voting.”

Sport’s gender pay gap problem

While all four of tennis’s Grand Slam tournaments now award equal prize money for men and women, there are other tournaments in the sport that have yet to catch up.

At this year’s Western & Southern Open in Cincinnati, men’s singles champion Novak Djokovic took home $1.02 million, while women’s champion Coco Gauff earned $454,000.

The WTA announced in June that it had established a pathway to attain equal prize money at all tennis tournaments by 2033.

Other sports are trailing behind, however, when it comes to closing or narrowing their own gender pay gaps.

In 2017, a study by BBC Sport found that 35 out of 44 sports pay men and women equal prize money—meaning 20% of sports had a gender pay gap for their elite athletes. The broadcaster contacted the governing bodies of 68 different sports, but only 55 responded, and not all of those who did respond paid prize money.

Meanwhile, in Forbes’s 2023 ranking of the world’s highest-paid athletes, only one woman broke into the top 50: Serena Williams, who the publication said earned an estimated $45.3 million in the 12 months to May.

Soccer’s pay gap was brought to light once more during the 2023 Women’s World Cup this summer. The tournament’s total prize pot amounted to $110 million, compared with $440 million up for grabs at the men’s World Cup in Qatar last year.

While payouts from governing body FIFA are still unequal, the U.S. women’s soccer team achieved pay parity last year when their male counterparts agreed to pool their prize money and split it equally among both teams.