While some sporting brands used International Women's Day to launch their Women's World Cup team kits, lawyers representing the world-champion US team were on their way to a California courthouse to file a landmark lawsuit that would rock the sport.

Instructed by the 28 members of the women's national team, they filed a suit accusing the US Soccer Federation of gender discrimination, alleging that it pays them less than their male counterparts.

"As players, we deserved to be paid equally for our work, regardless of our gender," star striker Alex Morgan said in a statement, but as she is well aware, deserving such treatment and actually getting it are two very different things.

Female players in other countries have endured often humiliating public squabbles before, and the American lawsuit marks a new front in the battle for equality with the World Cup in France less than three months away.

"They sacrifice their whole lives to play for their country, they're together and play more games than the men's team and they've been more successful," said Ireland striker Stephanie Roche.

"They are more like a club team in some ways, they play that many games. I think they have proven that they are equal, they have brought success and therefore have every right to demand equality," she added.

Roche, who scored a spectacular goal that was nominated for FIFA's Puskas award in 2014 and ultimately came second to James Rodriguez, was part of the Irish team that revealed how female players were forced to change in toilets as they sought to resolve a dispute with the Football Association of Ireland.

Such disputes are not new - Denmark's dream of making it to the World Cup effectively died when they boycotted a 2017 game against Sweden during a dispute with their football association.

That decision led to a points deduction which cost them the chance of winning their qualifying group, and they lost a playoff to the Netherlands.

The timing of the American suit could have been better for world governing body FIFA, which launched the poster it will use to publicise the 24-nation tournament on the same day.

The Zurich-based organisation also announced that it will hold its first Global Women's Football Convention in Paris ahead of the World Cup which begins on June 7, but all this was overshadowed by the breaking news from the American camp.

Winners of four Olympic gold medals and three of the seven World Cups that have been held to date, the U.S. women's team are ranked first in the world and have never been lower than second, while the American men are currently 25th.

Their squad boasts some of the biggest and most marketable names in the game such as Alex Morgan and Carli Lloyd, and Ireland's Roche, who plays for C.F. Florentina in Italy, says that she expects the Americans to remain steadfast.

"It's not something any team wants to have to deal with before a World Cup, but when a team is united by stuff like this I believe it can bring them together more off the pitch, and they can then bring that onto the pitch," she explained.

"Their players are all pros, so I've no doubt they will prepare well and be ready and focused for the World Cup, hopefully with the backing of their federation."

Equality has long been an issue simmering in the women's game, and it isn't going to go away.
Accepting the Diamond Ball for Sweden's best female player in 2018 at a gala awards dinner, defender Nilla

Fischer issued a clarion call to men to get behind the women's game.

"It's time to get in the game because equality is something that benefits us all, but it's something we have to do together," Fischer said.