One thing that has constantly cropped up in discussions about the future of European rugby is the threat, if not naked then certainly in varying degrees of undress, that players will be withheld from international duty by the English and/or French clubs unless their respective unions acquiesce.
It's surprising that it has been repeated so often without being critically assessed. Firstly, there are, of course, the requirements of the International Rugby Board Regulations on player release which you can read HERE (specifically, it's Regulation 9). Under IRB Bye-Law 7, there is a binding agreement between the IRB and the Rugby Football Union (RFU) to obey these and other IRB Regulations, and the RFU agrees to bind any and all rugby organisations under its jurisdiction in like fashion. The RFU does so in its Regulations, specifically Regulation 2, which you can read HERE. Premiership Rugby Limited, and its constituent clubs, are bound to obey those regulations.
Secondly, and in a belt-and-braces approach, there is a binding agreement between Premiership Rugby Limited and the RFU that players will be released for international duty above and beyond the requirements of the IRB Regulations, details of which Long-Term Agreement you can read HERE. Notably, in all the ongoing kerfuffle, it requires that England players are rested by their teams - a plank in one's own eye ignored while pointing out the mote in others. Be that as it may, the teams cannot withhold their players from the international duty agreed under without breaking that agreement. As it is the same agreement giving them the right to sell broadcasting rights, which is the origin of most of this sorry mess, one doubts they'd be eager to see it torn up. It runs until June 30th 2016 - well after the next Rugby World Cup.
And lest there be any doubt, this point has been litigated. To no great astonishment, it was in Wales, where rugby seems on occasion to be less the national sport than a pretext for the real national sport of ferocious warfare over how rugby should be organised (a search of legal databases on rugby law turns up an entirely disproportionate number of results involving the Welsh Rugby Union (WRU) and its clubs and regions). Back in 2008, the Welsh regions were objecting to having to release players for a training session with Warren Gatland's Welsh team, Grand Slam winners of the previous Six Nations. They refused to release the players; and the WRU went to the IRB seeking a ruling. The IRB, interestingly, ruled that this was a private contractual dispute between the WRU and the regions. The WRU then sought an injunction compelling the regions to release the players on the grounds that there was a binding agreement between the regions and the WRU with which the regions had to comply.
The judge, Havelock-Allen QC, agreed in an unreported decision (the citation is  EWHC 3399 (QB)), finding that each region had a participation agreement with the WRU whereby it agreed to be bound by the IRB Regulations, including player release. Applying a more stringent test than would be usual in deciding the balance of convenience for an injunction, he found that since losing players and prestige would damage the WRU in a way that money could not compensate, then he would grant an injunction directing that the players be released to attend the training sessions. The report in the Welsh media at the time can be read HERE.
In the context of the Long-Term Agreement and the RFU Regulations, the parallel can plainly be seen.
So, that's why I wonder just why this keeps being put forward as a real risk when the plain victor on this point when it came to the crunch the last time out was the union, not the clubs.