The United States Women's National Soccer Team recently won the Women's World Cup for the fourth time. But the team's compensation remains the subject of considerable controversy.

Chants of "equal pay" erupted after the team's victory over the Netherlands and during its triumphant victory parade in New York City.

The women's team sued the U.S. Soccer Federation, its parent organization, in March over gender discrimination. That followed a wage discrimination complaint in 2016 with the Equal Employment Opportunity Commission.

Weeks after the team filed the lawsuit against U.S. Soccer, 35 senators called for equitable pay for the team in a letter to U.S. Soccer Federation President Carlos Cordeiro.

How to catch Alex Morgan, other U.S. women with Orlando Pride

Martin Fennelly column: Trump, U.S. women's team need an ice cream social

And several Democratic presidential candidates have taken up the team's cause.

Sen. Elizabeth Warren of Massachusetts, a presidential candidate, signed the letter and tweeted her support.

"The @USWNT is #1 in the world & contributes higher revenues for @USSoccer than the men's team, but they're still paid a fraction of what the men earn," Warren said. "Women deserve equal pay for equal (or better!) work in offices, factories, AND on the soccer field."

We wanted to take a closer look at the issue.

We found evidence supporting the team's case, and most of the experts we contacted for this fact-check considered Warren's tweet to be well-grounded. But there are other parts of the story that make the narrative more complicated. Ultimately, the compensation formulas are too variable — and too little is known about the governing documents — for us to put Warren's claim on the Truth-O-Meter.

Here's the bottom line of what we found:

During the three years following the 2015 Women's World Cup, the women's team brought in slightly more revenue from games than the men's team did. While marketing and sponsorships are sold as a bundle, there are anecdotal signs that the women's brand is surging in popularity.

However, it's harder to say whether the women are ultimately paid less than the men, due to the lack of transparency and the complicated variables that feed into the compensation. Several experts said the reality may be murkier than a shouted catchphrase can capture.

"While Warren is 100% right that USWNT is No. 1 in the world, the economics portion of her tweet is more complex than the tweet suggests and the accuracy of her depiction depends on measurement tools that aren't noted in the tweet," said Michael McCann, a University of New Hampshire law professor who specializes in sports law.

What does the USWNT allege in its lawsuit?

The lawsuit, filed by 28 players on International Women's Day, alleges that U.S. Soccer pays the women's team less, gives them unequal playing conditions and does not promote their games as much as the men's team.

The women's team has won four World Cup titles while the men's team hasn't won any, the lawsuit points out. And if both teams played and won 20 "friendly" matches in a year, the women would earn a maximum of $99,000 and the men would earn an average of $263,320, according to the suit. In this scenario, players on the women's team would earn 38% of what the men earn.

Jeffrey Kessler, a lawyer representing the women's team, told PolitiFact that Warren's statement is "entirely accurate."

"The women earn more revenues than the men, are world champions and make substantially less," Kessler said. "It is legally and morally wrong."

A week after the women's team filed their lawsuit against U.S. Soccer, Cordeiro responded in an open letter that he tweeted out. It said the federation serves as a champion for women's soccer.

"U.S. Soccer believes that all female athletes deserve fair and equitable pay, and we strive to meet this core value at all times," he said.

Does the women's team bring in more revenue?

In the eight FIFA World Cup tournaments held on the women's side, the U.S. women's team has won four and either came in second or third place in the others. By contrast, there have been 21 FIFA World Cup tournaments, but the U.S. men's team did not qualify for about half the tournaments, and only placed as high as third once — in 1930.

There are certain areas in which the women have generated higher revenue than the men have in recent years.

Let's start with revenue from games, which have recently accounted for about one-quarter of the federation's gross revenues.

When the Wall Street Journal audited the federation's financial reports, it found that the U.S. women's soccer games earned more than the men's games, in total, during three years after the women's team won the World Cup in 2015.

Specifically, from 2016-18, the women's team brought in $50.8 million in revenue, while the men's team brought in $49.9 million. That's a difference of less than 2% in the women's favor.

Looking year by year, 2016 was actually the only year in which the women's team generated more revenue from games — $24.11 million, compared to $22.24 million for the men. In 2017, both teams brought in about the same revenue at $14.61 million, and in 2018, the men's team brought in $13 million compared to the women's $12.03 million.

This pattern marked a reversal from prior years: In 2014 and 2015, the men's team earned $8.31 million and $11.71 million more than the women's team, respectively.

Beyond game revenue, U.S. Soccer brings in money through marketing and sponsorships; this category accounts for about half of the total revenues in recent years. Marketing and sponsorships, which includes the sale of broadcast rights, is hard to credit to either the men or women, because these transactions are made as a bundle, not separately for each team.

That said, there is anecdotal evidence that the on-the-field success of the women's team has given the federation a windfall.

"The World Cup final in 2015 and this year's final set records for U.S. viewership for a soccer game," said Ryan J. Lake, a sports-law specialist at the Lake Law Group in Denver. "This year's final did about 20 times better than the men's World Cup final last summer, in the U.S." (The 2018 men's World Cup final pitted France vs. Croatia.)

In addition, Nike has announced that women's jersey sales are setting records for either men or women.

These achievements are even more notable given what the women's team argues in the lawsuit: that U.S. Soccer has given them fewer resources and does not announce their games with enough time to get the biggest audience.

How are the players paid?

Player compensation is more complicated to calculate because many variables are involved — and less information has been made public about the current compensation mechanism.

Earnings for both men and women are governed by collective bargaining agreements, with a player's eventual earnings affected by the number of games played and whether the team wins or loses.

In the lawsuit, the women's team said that if each team were to win 20 exhibition games in a year, "female WNT players would earn a maximum of $99,000 or $4,905 per game, while similarly situated male MNT players would earn an average of $263,320 or $13,166 per game."

However, this calculation was made under the old collective bargaining agreement.

PolitiFact was unable to obtain a copy of the current bargaining agreement, which has not been released publicly. The Associated Press reported that the 2017 agreement for the women's team, which runs through 2021, includes "raises in base pay and bonuses as well as better provisions for travel and accommodations, including increased per diems."

In fact, under the new agreement, women's team members are paid a guaranteed salary and then collect bonuses on top of that, while the men's team players are paid only a bonus, the Associated Press reported. So the women have the security of a guaranteed floor.

Our friends at the Washington Post Fact Checker did obtain a copy of the new agreement. When they calculated the same 20-game scenario as the lawsuit did for the old agreement, they found that a women's team player would now earn "$28,333 less, or about 89 percent of the compensation of a similarly situated men's team player."

In other words, by this calculation at least, a women's team player would earn less than an equivalent men's team player — about 11 percent less.

But that comparison is heavily dependent on such factors as games played and won. "If both teams lost all 20 games, the players would make the same amount," the Fact Checker calculated. "That's because the men earn a $5,000 bonus when they lose and the women have a $100,000 base salary."

What about World Cup compensation?

The most unbalanced element of the men's and women's teams' compensation is the money players get for playing in and winning the World Cup. But this is not directly at issue in the suit, because it's ultimately shaped more by the international soccer governing body, FIFA, than by U.S. Soccer.

Part of the issue is the overall state of the women's and men's soccer games around the world. More money flows into the men's professional leagues around the world, and that approach funnels down to the national teams.

For the 2018 men's World Cup, the prize money was $400 million, compared to $30 million for the Women's World Cup in 2019. Given the vast difference in total funds available to allocate, it's essentially guaranteed that the women would end up with far less prize money than the men could have — even though the women won the championship.

And this particular disparity is destined to continue.

"FIFA announced the prize money would be $440 million in 2020 in Qatar, and $60 million for the 2023 Women's World Cup," said Cheryl Cooky, a Purdue University professor of American studies who specializes in sports. "While doubling the prize money for the women's tournament, FIFA did so while also raising the prize money for the men. The women's prize money is still only 14% of the men's."

Areas of dispute beyond money

While Warren's tweet focused on the money differences, it's worth adding that the lawsuit also lays out disparities that aren't strictly economic.

"The women's national team players raise issues not just about compensation but also safe work environments (they are put at risk more frequently by having to play on non-grass fields than the male players); travel (the men fly charter, while the women fly commercial); ticket prices (which are lower for WNT games compared to the men); and marketing efforts (less of an investment in the women's game)," said Ellen J. Staurowsky, a professor of sport management at Drexel University.

One notable difference, Cooky said, is that when the women returned from their 2015 World Cup win, the games for the women's professional league, the National Women's Soccer League, were broadcast on YouTube. The men's league, Major League Soccer, had a multi-year, multi-million contract to broadcast their games on major TV networks like ESPN and Fox Sports.

This disparity reflects the worldwide gender inequities in soccer, and sports generally, Staurowsky said.

"When the U.S. Soccer Federation defends its differential treatment of women players by pointing to market arguments, they fuel old stereotypes that people are not interested in women's sport and women's sport is not interesting," she said. U.S. Soccer is "failing to capitalize fully on arguably one of the most marketable teams in recent memory."