Some clubs offer improved contractual terms if individuals agree before signing that they will not make themselves available for their nations at the World Cup. Other clubs write disproportionate financial penalties into contracts should international players feature at a World Cup.
And then there are the suspicions held by coaches of Tier Two international sides and other global administrators that some clubs just make verbal, plausibly deniable threats about the consequences of playing at a World Cup.
It is a minefield and one the IRB is effectively powerless to stop as they effectively admitted when they said they can only intervene if the affected nation makes a complaint.
The Pacific Islands need open, functional relationships with Europe's leading clubs and whistleblowing could be disastrous: the top sides will squeeze tighter and either make it a prerequisite that Pacific Island and other Tier Two players give up international rugby or they won't contract them.
The sad fact is that while Clause 9 around player release is legally binding and European clubs are happy to comply with it throughout November, serious doubt exists whether this will be the case come the cup because of the length of the tournament.
European domestic competitions will be in full flow and leading clubs wouldn't dare pressure Tier One players to boycott. But players from lower ranked nations can be more easily bullied and manipulated and the great losers once again will be the Pacific Island test sides.