Global stars including England captain Owen Farrell and Ireland fly-half Johnny Sexton have warned of serious player welfare and integrity concerns over World Rugby's proposed new competition structure.
The International Rugby Players' Council held a detailed conference call this week that included nine of the world's top 10 Test team captains dialling in.
A new global season is due to kick off next year, running until 2032.
— InternationalRugbyPlayers (@IntRugbyPlayers) February 28, 2019
Discussions, meanwhile, have also taken place about a new World League that would combine 12 international sides from both hemispheres in a competition running through summer and autumn and culminating with play-offs and a final.
The IRPC said players were "united in their concern" about issues such as player-load challenges from playing multiple Tests across different time zones in consecutive weeks, increased conflicts between club and country demands, plus potential impact on the World Cup and British and Irish Lions tours.
The IRPC also claimed that promotion and relegation will not form part of the new proposal, saying it would prevent Tier Two and emerging nations from accessing top level competitive matches.
It is understood that any World League would have the intention of featuring England, Wales, Scotland, Ireland, France, Italy, New Zealand, Australia, South Africa and Argentina, plus Japan and the United States, who could be invited to join the Rugby Championship.
But if no promotion and relegation is sanctioned, then it could mean countries like Georgia, Samoa, Fiji and Tonga being isolated.
"It seems like a commercial deal on the future of the game is being negotiated at a rapid pace with little consideration given to the important points we raised with World Rugby in November," Sexton said, in a statement released by the IRPC.
"The issue of player-load has never been so topical. However, it needs to be properly understood."
Farrell, meanwhile, added: "Players are definitely open to discussing a new global season, but what we develop has to work with the club game in order to reduce conflict, deal with player release issues and make sure their welfare is looked after."
Farrell's England team-mate Ben Youngs wants the clubs to be thought of.
"You look at it and straight away you are thinking, 'Player welfare, more matches, how does it fit into the schedule that has already been changed anyway to make the season longer, how are your clubs going to feel about that?'" said the scrum-half, 29.
"There is a huge amount that needs to be worked out before it could ever get to that stage. You have certain countries who aren't involved when you are looking to grow the game. If you are going to grow the game surely you want as many of these countries in as possible?"
Asked if other competitions would have to be sacrificed from the rugby calendar to accommodate the proposed World League, he then responded: "I believe so.
"You will spend more time away from your club; how does that fit with them?"
England's George Kruis stressed the importance of considering modern players' mental health, which has perhaps been given greater relevance by former team-mate Joe Marler previously missing international duty because of his urgent need to rest.
"The players have to be heard and it's massively important that they are, especially at international level where they are expected to play — and don't get me wrong they want to play — big games," Kruis said.
"Physically and mentally then they go back to their clubs and they are relied on because they are the better players. For me it's about player welfare and managing the expectation, finding ways to look at the physical and mental load; often the latter gets overlooked."
World Rugby said its commitment to player welfare matters is "unwavering."
In a statement, the sport's governing body said: "World Rugby recognises and values the importance of player considerations and input into the annual international competition discussions.
"However, the manner the International Rugby Players (IRP) organisation has expressed these is surprising, given regular engagement throughout this ongoing process.
"World Rugby's commitment to player welfare matters is unwavering, and we will continue to engage and give full consideration to the welfare of players within the ongoing discussions.
"It is inappropriate to comment on specifics while wider stakeholder consultation, including with IRP, is ongoing.
"However, it is important to note that some assumptions made in the statement regarding the proposed competition structure are inaccurate, and that important matters such as playing load and emerging nation opportunities are at the heart of constructive dialogue on the overall concept.
"As instructed by our executive committee and the Unions, we remain committed to a process of constructive dialogue with all stakeholders, including the IRP, to deliver a model that ensures the best-possible competition and commercial outcomes for all."