The rugby unions of New Zealand, South Africa, Ireland, England, Scotland, France and Italy have also signed up to the ban and warned players considering joining the rebel competition to exercise "extreme caution".
The R360 league, fronted by former England centre Mike Tindall, is due to launch in 2026 and media reports have linked it with big-money offers for top rugby union and league players.
"As a group of national rugby unions, we are urging extreme caution for players and support staff considering joining the proposed R360 competition," the unions said in a rare joint statement.
"International rugby and our major competitions remain the financial and cultural engine that sustains every level of the game — from grassroots participation to elite performance.
"Undermining that ecosystem could be enormously harmful to the health of our sport."
Wales, Argentina, Fiji and Japan are the most notable non-signatories to the statement, along with Women's World Cup finalists Canada, though the Welsh Rugby Union expressed support for the statement.
The unions say R360 has given them no indication as to how it plans to manage player welfare, how players would fulfil their aspirations of representing their countries, or how the competition would coexist with the international and domestic calendars.
They also say that the R360 model appears designed to generate profits and return them to a very small elite, and those behind the proposed competition have not engaged with all unions to explain their business and operating model.
"Each of the national unions will therefore be advising men's and women's players that participation in R360 would make them ineligible for international selection," the statement concluded.
In response R360 said it wanted to work collaboratively.
It added that player welfare was one of the key reasons for creating the series, which it said would greatly reduce player load and capture the attention of a new generation of fans globally.
"It's not always easy to embrace new opportunities, but as we've seen throughout history, it's essential for any sport to grow," a statement said.
The league hopes to establish eight men's teams and four women's teams who will compete in a condensed season format in 'grand prix' style events around the world in cities such as London, Miami, Tokyo and Lisbon.
As many as 200 players are believed to have signed pre-contracts worth up to $A1.5 million, but as yet none of them have made their interest public, while there are also no details of who is investing into the event.
with PA
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