Fifty years ago, Billie Jean King walked into the offices of the U.S. Open and demanded that they pay women the same amount as men. She had a very powerful bargaining tool in her pocket: A sponsor, Ban deodorant, that was willing to put forward the $55,000 needed to close the wage gap. The U.S. Open agreed, and the New York Times authored a headline, “Tennis Decides All Women are Created Equal, Too.”

It turns out, that headline might have been just a tad premature.

It took 34 years for all four tennis majors to offer equal prize money — the Australian Open finally made the switch for good in 2001, and the French Open and Wimbledon followed suit in 2006 and 2007, respectively, thanks in no small part to the advocacy of Venus Williams. But even that wasn’t the end of the fight.

Today in tennis, women still face sexism on a daily basis. That was particularly on display this clay-court season, where the two big Roland Garros lead-up events in Madrid and Rome were rife with disrespect for women. The trend continued at the French Open, where women were regularly treated like a warm-up act for the men. And a look at the prize money pools outside of the four majors show that while women’s sports are seeing significant growth globally, the wage gap in tennis is actually widening. Here is a New York Times report on the subject:

The best tennis players in the world descend this week on Rome, where men and women will play in the same best-of-three-sets format, on the same courts and in the same tournament, which sells one same-price ticket for both men’s matches and women’s matches.

There is one massive difference between the two competitions, however: Men will compete for $8.5 million while the women will compete for $3.9 million.

The huge pay discrepancy comes after two months of tennis that included three similarly significant tournaments in California, Florida and Madrid that featured men and women competing for the same amount of prize money. Men and women also get paid the same at the four Grand Slam tournaments, where men play best of five sets and the women play best of three.

But not in Rome at the Italian Open. And not yet in the Cincinnati suburbs at the Western & Southern Open. Or in Canada, at the National Bank Open, where the men and women alternate between Toronto and Montreal each year.

Angelo Binaghi, the chief executive of Italy’s tennis federation, announced recently that the Italian Open was committed to achieving pay equity by 2025 “to align itself with other major events on the circuit,” even though an expanded format will bring in additional money this year. For the next two editions of the tournament, women will have to do the same work for a lot less pay, which makes them feel, well, not great.

“I don’t know why it’s not equal right now,” said Paula Badosa, a 25-year-old from Spain who is among the leaders of a nascent player organization, the Professional Tennis Players Association. “They don’t inform us. They say this is what you get and you have to play.”

A spokesman for the Italian federation did not make Binaghi available for an interview.

“It’s really frustrating,” Ons Jabeur, who made two Grand Slam finals last year and is seeded fourth in Rome, said during an interview Tuesday. “It’s time for change. It’s time for the tournament to do better.”

Steve Simon, the chairman and chief executive of the WTA Tour, which organizes the women’s circuit on behalf of the tournament owners and players, said the disparate prize money was a reflection of a market that values men’s sports more highly than women’s, especially for sponsorships and media rights. He said the organization was working toward a solution that would strive to achieve pay equity at all of tennis’s biggest events in the coming years.

“There is still a long way to go but we are seeing progress,” Simon said in an interview Monday.

The explanations — and blame — for women in tennis continuing to be so shortchanged include ingrained chauvinism, bad agreements with tournament owners and the eat-what-you-kill nature of the sports business, where owners, officials and organizers often blame the athletes (rather than their incompetence) for not generating enough revenue. Then they use it as an excuse not to invest in the sport and keep athlete pay and prize money low.

In tennis, women often receive second billing in mixed tournaments — less desirable schedules on smaller courts, sometimes even lesser hotels. In Madrid last week, the participants in the women’s doubles final did not get a chance to speak during the awards ceremony. The men did.

Organizers often tell the women they lack the star power of the men. At the French Open last year, Amélie Mauresmo, the tournament director and a former world No. 1 in singles, scheduled just one women’s match in the featured nighttime slot compared with nine men’s matches, then explained that the men’s game had “more attraction” and appeal than the women’s game. She later apologized, but when second billing can make it harder for women to achieve stardom, this self-fulfilling prophecy can lead to lower pay.

In March, Denis Shapovalov of Canada, currently ranked 27th, published an essay in The Players’ Tribune criticizing the sport’s leaders for not being more unified.

“I think some people might think of gender equality as mere political correctness,” wrote Shapovalov, whose mother has coached him and whose girlfriend, Mirjam Bjorklund of Sweden, plays on the women’s tour. “Deep down they don’t feel that women deserve as much.”

The WTA has committed some unforced errors. At the most important mixed tournaments, attendance is mandatory for women and men. The WTA requires participation at tournaments only in Indian Wells, Calif.; Miami Gardens, Fla.; Madrid; and Beijing, but not in Rome, Canada or Ohio, even though those events rank just behind the Grand Slam events in importance. Also, the WTA awards slightly fewer ranking points than the men’s tour does in Rome, Canada and Ohio, where the women’s champion receives 900 points compared with 1,000 for the men.

These minor differences have given tournament officials an excuse for paying women so much less, even though nearly all of the top women play the big optional events, unless they are injured. Organizers, however, say that without mandatory participation they can’t market the tournament as effectively, so local sponsors and media companies will not pay as much.

“It’s time for change. It’s time for the tournament to do better,” said Ons Jabeur, who is seeded fourth in Rome.Credit…Marijan Murat/DPA, via Associated Press

Marc-Antoine Farly, a spokesman for Tennis Canada, cited that difference when asked recently why the National Bank Open offered men $5.9 million last year, compared with $2.53 million for the women. Despite that difference, Farly said, “gender equity is very important for our organization.” He pointed to Tennis Canada’s recently released plan to seek gender equity at all levels during the next five years and to offer equal prize money at the National Bank Open by 2027. “Over the next few years, Tennis Canada fully intends to be a leading voice with the WTA on a development plan to close the WTA/ATP prize money gap.”

Like most aspects of the tennis business, the formula for prize money requires a somewhat complicated explanation. Tournament owners guarantee a portion of revenues from tickets, domestic media rights and sponsorship sales for prize money. The tours contribute a portion using money from their own media rights and sponsorship deals as well as the fees the tournament owners pay the tours to acquire the licenses for the events. Simon said the WTA brings in substantially less money than the men’s circuit, the ATP Tour, which means it has substantially less money to contribute to prize money.

That said, if equal prize money is important to tournament owners, they can choose to pay it. That is what the BNP Paribas Open at Indian Wells, owned by the computer technology billionaire Larry Ellison, has agreed to do for more than a decade under his contract with the WTA.

“The tournament views the event as a single product,” said Matt Van Tuinen, a spokesman for the tournament. “Paying them equally is the right thing to do.”

Same goes for IMG, the sports and entertainment conglomerate that owns both the Miami Open and the Madrid Open. Both pay equally.

In addition to Italy’s and Canada’s tennis federations, the United States Tennis Association, which has long bragged about its leadership in pay equity, did not award equal prize money at the Western & Southern Open, the main tuneup for the U.S. Open. Last year, men competed in Mason, Ohio, for $6.28 million. Women competed for $2.53 million. The U.S. Open became the first of the Grand Slam tournaments to offer equal prize money, in 1973, and will celebrate the 50th anniversary of the event in grand fashion this summer. The U.S.T.A. ran the Cincinnati-area tournament for more than a decade.

Chris Widmaier, a spokesman for the organization, said the prize money was “dictated by the commensurate level of the competition as determined by each tour.”

In other words, since the Western & Southern was not a mandatory WTA event and the women competed for 10 percent less rankings points, paying them roughly 40 cents for each dollar the men received was justified.

The U.S.T.A. last summer announced it was selling the tournament to Ben Navarro, the South Carolina financier and tennis enthusiast. Through a spokesman, he declined to be interviewed for this article.

Help may be on the way.

Earlier this year, CVC Capital Partners, the private equity firm, bought 20 percent of a WTA commercial subsidiary for $150 million. The investment, which will be used to enhance sales and marketing efforts, combined with a strategic plan being finalized that would eliminate the discrepancies between the men’s and women’s competitions at the mixed events, is supposed to help the WTA grow its revenues. That will allow the tour to contribute more to prize money and hopefully get tournament organizers to commit to pay equity in the coming years.

The plan requires some patience, which is running thin among the players.

“I don’t see why we have to wait,” Jabeur said.