The player organisation set up by Djokovic and Canada's Vasek Pospisil, supported by Kyrgios, has launched legal action against tennis' governing bodies.
Founded in 2021, the Professional Tennis Players Association (PTPA) cites its mission as supporting and safeguarding professional tennis players.
But it has found driving change from outside the system very difficult and is now taking a legal route against the ATP and WTA, which organise the men's and women's tours, the International Tennis Federation, which runs team competitions and much else, and the International Tennis Integrity Agency, which oversees the sport's anti-doping and anti-corruption system.
Twelve current and former players, including Djokovic, Pospisil and Kyrgios, are listed as plaintiffs along with the PTPA.
A statement read: "Following years of good-faith efforts to reform professional tennis, the Professional Tennis Players Association (PTPA) has taken decisive legal action.
"Today, the PTPA, alongside over a dozen professional tennis players and on behalf of the entire player population, and renowned international law firm and historical player advocates Weil, Gotshal & Manges LLP, initiated a series of legal actions in the US, UK and EU against the sport's governing bodies."
The statement added: "The lawsuits expose systemic abuse, anti-competitive practices, and a blatant disregard for player welfare that have persisted for decades."
Among the PTPA's complaints are the suppression of competition between tournaments, which it says reduces prize money, a draconian ranking points system, an unsustainable schedule and financial exploitation of players.
It also accused the governing bodies of disregarding player welfare by forcing athletes to compete late at night and in extreme heat, while the PTPA branded anti-doping practices an invasion of privacy.
Pospisil, a former Wimbledon doubles champion and quarter-finalist in singles, said: "This is not just about money, it's about fairness, safety, and basic human dignity.
"I'm one of the more fortunate players and I've still had to sleep in my car when travelling to matches early on in my career. Imagine an NFL player being told that he had to sleep in his car at an away game? It's absurd and would never happen, obviously. No other major sport treats its athletes this way.
"The governing bodies force us into unfair contracts, impose inhumane schedules, and punish us for speaking out. The legal actions taken today are about fixing tennis for today's players and future generations."
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