The body that organises the Heineken Cup has questioned the validity of BT Vision's new television deal with England's top clubs.
BT announced it had won the rights to broadcast the Premiership from next season, as well as English clubs in European matches from 2014.
But European Rugby Cup (ERC) says it has already given exclusive coverage of European matches to BSkyB.
Premier Rugby, which advises English clubs, insists its contract is valid.
Premier Rugby's new agreement with BT, divided into a deal to show Premiership rugby from next season and European club rugby from the start of the 2014-15 campaign, is worth up to £152m.
However, ERC insists it has also agreed a deal with BSkyB for exclusive coverage of European club rugby from the start of the 2014-15 season.
ERC claims that Premier Rugby's European deal with BT is "in breach both of International Rugby Board regulations and of a mandate from the ERC Board itself".
An ERC statement continued: "European club rugby's six participant unions have granted the authority to sell broadcast rights to its tournaments solely to ERC.
"It was unanimously agreed at an ERC Board meeting on 6 June, 2012 that ERC would conclude a new four-year agreement with Sky Sports. Premiership Rugby was party to that decision."
But Premier Rugby argues that ERC's right to negotiate broadcast deals on behalf of unions is only valid until 2014.
"On 27 July, 2012, ERC was reminded of this in writing and this was copied to Sky Sports," it said in a statement.
"We also note ERC's reference to its board meeting on 6 June, 2012. No specific broadcast deal was presented or voted on at this or any subsequent ERC board meeting. In any case, any such deal could not have included matches involving Premiership Rugby clubs.
"ERC's suggestion that Premiership Rugby may be in breach of IRB regulations is wrong."
There has been long-running tension between the ERC and English and French clubs, who have announced they will pull out of ERC once the current agreement governing their participation runs out at the end of the 2013-14 season.
This effectively means they are withdrawing from the Heineken Cup after the 2014 final, although the planned move has been seen as a negotiating tactic.
This is because both the French and English clubs want changes to the way European rugby union's blue riband club tournament, in which Irish province Leinster are the current champions, is run.
They want a new system that would reduce the number of RaboDirect Pro12 teams that qualify for the Heineken Cup, removing the current guarantee that leads to Scotland, Ireland, Wales and Italy all being ensured representation.
There is no relegation from the Pro12 and the English and French sides argue this gives Irish teams, in particular, an advantage, because they can rest players for league matches to keep them fresh for Europe without facing any real consequences.