World number one Novak Djokovic has resigned as president of the ATP player council to front a new association aiming to increase the power of the players.
But he faces opposition from Rafael Nadal and Roger Federer, who remain members of the council.
Britain’s Andy Murray has not yet joined the male-only association and has called for the WTA to be involved.
The first players to sign up for the Professional Tennis Players’ Association met on Saturday at the Billie Jean King National Tennis Centre in New York, where the US Open begins on Monday.
Between 60 and 70 players posed for a photo posted on social media by the Canadian Vasek Pospisil, who has been a driving force behind the new association along with Djokovic.
Djokovic first raised the idea of a players’ union at the 2018 Australian Open. Since then a number of his peers have been agitating for a greater share of the revenue generated by the Grand Slams, in particular.
“I have read in the letter from the ATP that they think the ATP cannot co-exist with this association. I have to respectfully disagree,” Djokovic said after winning the Western and Southern Open on Saturday.
“Legally, we are 100% safe, and we are allowed to form the player association. We are not calling for boycotts, we are not forming parallel tours. This is an important step for players, and for the sport as well.
“We just want to have our own organisation, that is 100% ours. We are definitely going to try and work with ATP, and all the governing bodies.”
At last year’s US Open, the idea of an association of both male and female players was gathering momentum. The fact this is a male-only venture is one of the reasons Murray will not yet be joining.
“I’m not totally against a player union,” the former world number one said.
“But I feel like the current management that are in place should be given some time to implement their vision, and I feel like that would send a much more powerful message if the WTA were on board with it as well.”
World number two Nadal, who is not playing in the US Open, had already made clear his opposition in a post on social media.
“The world is living a difficult and complicated situation. I personally believe these are times to be calm and work all of us together in the same direction,” the Spaniard said.
“It is time for unity, not for separation. These are moments where big things can be achieved as long as the world of tennis is united.”
Shortly afterwards, Federer, who is also absent from New York, shared Nadal’s post and added: “I agree. These are uncertain and challenging times, but I believe it’s critical for us to stand united as players, and as a sport, to pave the best way forward.”
Since the ATP Tour sprang into life in 1990, the players and the tournaments have, in theory, had an equal voice. There are three player representatives and three tournament representatives on the ATP board. If there is deadlock, the chairman has the right to a casting vote.
Former top-20 player Andrea Gaudenzi took over as ATP chairman in January.
Disappointment in the leadership is one of the reasons that 2016 Wimbledon runner-up Milos Raonic says he will join the new association.
“A lot of us were kept in the dark by our leadership for six months,” the Canadian said.
“We have a former player leading us. I hope they step up and they work a bit more with the players like we would have expected from a former player.”
But British number one Dan Evans told BBC Sport he will not be signing up.
“It’s not great timing, and I don’t believe in what they are saying, to be honest,” he said.
“A lot of players do [seem to be in support], but with not a lot of information. We just have to be a little bit careful what we could turn the tour into if this does happen.”
In a statement, the ATP Tour said: “We recognise the challenges that our members face in today’s circumstances. However, we strongly believe that now is a time for unity, rather than internal division.
“We remain unwavering in our commitment to deliver for our players across all areas of our business, ensuring they receive maximum benefit from their years on Tour, and that their voices are heard.”
The Tour also received support from the WTA, the ITF and the four Grand Slams, who said in a statement: “It is a time for even greater collaboration, not division; a time to consider and act in the best interests of the sport, now and for the future. When we work together, we are a stronger sport.”