The Professional Footballers' Association has joined a legal action against Fifa over the "overloaded and unworkable" football calendar.
The PFA are co-claimants with the French players' union in the claim filed at the Brussels court of commerce, with the support of the European office of players' union Fifpro.
It is "challenging the legality of Fifa's decisions to unilaterally set the international match calendar and, in particular, the decision to create and schedule the Fifa Club World Cup 2025".
There are scheduled to be 12 European representatives at the expanded Club World Cup, to be held in the United States from 15 June-13 July 2025.
The PFA says it has "joined a legal case which will seek to challenge the structures of the current football calendar by enforcing the legal rights of players to take guaranteed and protected breaks".
The English players' union believes the scheduling of the tournament, which was confirmed by the Fifa Council in December 2022, is a "tipping point for the football calendar and the ability of players to be able to take meaningful breaks between seasons".
Fifa recently rejected claims that Fifpro and the World Leagues Association were not consulted over plans to host the competition.
World football's governing body also said that, while it was open to talks, it had no intention of altering next year’s Club World Cup, despite the threat of legal action.
"Everyone across football knows that the fixture calendar is broken to the point that it has now become unworkable," said PFA chief executive Maheta Molango.
“There are too many emerging instances across football where the rights of players, and the legal implications of decisions by governing bodies and competition organisers, are seen as something that can just be ignored.
“Players are not being listened to and they want to see action. As their union, we have a duty to intervene and to enforce their legal rights as employees. Ultimately, that time has now come.”
Molango has emailed 16,000 current and former PFA members from both the men’s and women’s game about the matter.
In the email he says the football calendar being "completely out of control" has an impact "felt across the game", adding it it not an issue that "only really impacts a few of the most ‘in demand’ players".
"It matters to all of us," he says.
The legal claim has asked the Brussels court of commerce to refer the case to the European Court of Justice (ECJ) for a preliminary ruling on the interpretation of EU law as it relates to footballers’ rights.
A PFA statement said: “The ECJ would then send the case back to the court in Belgium for a final ruling which could have a significant and far-reaching impact on the way the football calendar is structured."
Next season, all three European club competitions will be expanded to 36 teams. The Champions League and Europa League will have eight first-phase games compared to the six in the 2023-24 campaign.
The PFA highlighted that for some of its members "the 2024-25 season is set to roll almost seamlessly into the 2025-26 season".
The next Premier League campaign finishes on 25 May, 2025 before the Champions League final on 31 May.
There will then by a window of international games from 2-10 June before the start of the extended Fifa Club World Cup.
"Players will then be likely to have club commitments ahead of the 2025-26 season, potentially including the FA Community Shield, with the Premier League season scheduled to kick off again in mid-August," said the PFA.
David Terrier, the president of Fifpro Europe, said the legal route was being taken "since all attempts at dialogue have failed".
He added: "It's not a question of stigmatising a particular competition, but of denouncing both the underlying problem and the straw that broke the camel's back."
BBC Sport senior football news reporter Nick Mash*ter
This should not come as a surprise.
It may not be the only legal avenue which is pursued but the tipping point of the extended Club World Club next summer means it is the most pertinent and important one to start with.
This is the culmination of more than 12 months of work between leagues and unions, spearheaded by PFA chief executive Maheta Molango.
There is a feeling the PFA cannot go back into clubs at the start of next season and look players in the eye without having done something to protect them.
If players reach the Champions League final next season with their club – on 31 May in Munich – then play in the expanded and contentious Club World Cup in the summer of 2025, they face more pressure on their bodies.
The Club World Cup end date of 13 July is likely to be just four weeks before the start of the 2025-26 Premier League season.
The PFA then believes any players involved with international commitments would not have a break between seasons, and placing the burden on clubs to resolve the issue and rest players is viewed as unfair.
There is also the trickle down impact on the domestic calendar because of the decisions of Fifa and Uefa to expand competitions and calendars.
We have already seen the decision to scrap FA Cup replays – and there are valid arguments for and against that decision - so the change is happening right now. The decisions at the top have an influence on those lower down the domestic pyramid, not just the elite, and that should not be forgotten.
