You've definitely heard about the US Women's National Soccer Team. Here's the opening paragraph of their Wikipedia entry (with content from the US Women's National Team media guide):
"The team is the most successful in international women's soccer, winning three Women's World Cup titles (including the first ever Women's World Cup in 1991), four Olympic women's gold medals (including the first ever Olympic women's soccer tournament in 1996), eight CONCACAF Gold Cups, and ten Algarve Cups. It medaled in every single World Cup and Olympic tournament in women's soccer history from 1991 to 2015, before being knocked out in the quarterfinal of the 2016 Summer Olympics."
Not only are they the winningest team in women's soccer history, they also outperform the US Men's National Soccer Team in every available metric: victories, viewership, name recognition.
For example, according to Quartz, The women’s World Cup final drew more US network TV viewers than the men’s final: "The [2015 Women's World Cup Final] match brought in an estimated 21 to 23.5 million viewers on Fox. That’s considerably more than the the 2014 men’s final between Germany and Argentina, which garnered 17 million viewers on another US network station, ABC ... The 15.2 metered household rating is the highest ever for a soccer game in the US. It was the most-watched US soccer game in history, beating out US-Portugal on ESPN in the 2014 men’s World Cup."
The women have even begun to exceed the men in the metric that matters most in a free market: Revenue. (That's true in the US; worldwide, men's soccer is the bigger revenue generator.)
Even if they weren't outperforming, the US Women's National Soccer Team has a "Fair Pay Clause" in their collective bargaining agreement which should make the revenue piece a moot point. And, as if all of that weren't enough, their attorney has cited "the same argument used on behalf of men in figure skating, where the women produce more revenue than the men but prize money is distributed equally to 'do the right thing' according to those in charge."
Side note: Interesting that when men might be the lower paid party, an equal payout is considered the "right thing to do."
The women have recently filed suit again in an attempt to remedy the gender wage gap in their sport. Though there are many aspects to the complaint - which range from disparities in practice facilities, medical treatment, travel, training, and outright compensation - this is really at the heart of the matter, in language drawn straight from the complaint:
"The USSF, in fact, has admitted that it pays its female player employees less than its male player employees and has gone so far as to claim that 'market realities are such that the women do not deserve to be paid equally to the men.' The USSF admits to such purposeful gender discrimination even during times when the WNT earned more profit, played more games, won more games, earned more championships, and/or garnered higher television audiences."
"A comparison of the WNT and MNT pay shows that if each team played 20 friendlies in a year and each team won all twenty friendlies, female WNT players would earn a maximum of $99,000 or $4,950 per game, while similarly situated male MNT players would earn an average of $263,320 or $13,166 per game against the various levels of competition they would face."
This amounts to just 38 percent of the compensation of a similarly situated player on the men's team paid to women's team players who have outperformed their male counterparts.
“We very much believe it is our responsibility,” [WNT captain Megan] Rapinoe said, “not only for our team and for future U.S. players, but for players around the world — and frankly women all around the world — to feel like they have an ally in standing up for themselves, and fighting for what they believe in, and fighting for what they deserve and for what they feel like they have earned.”
Want to read more? You might have seen the flurry of press on the subject:
From The Philadelphia Inquirer: USWNT sues U.S. Soccer Federation, alleging Equal Pay Act discrimination
From WSJ (paywall): U.S. Women's Team Sues Soccer Federation, Alleging Discrimination
An editorial in the LA Times: U.S. women’s soccer outperforms the men in every way possible. Why are they paid less?