WRU Group Chief Executive David Moffett wants to restructure the Welsh game by next season, entering four regional sides in the Celtic League and European competitions.
Blanco, president of the French clubs' Ligue Nationale de Rugby, says that changes to the teams being entered for the Heineken Cup need the approval of all 12 members of the European Rugby Cup board.
Howard Thomas, chairman of England's Premier Rugby, has backed Blanco's stance.
The former French full back was speaking after attending Llanelli's Heineken Cup victory over Bourgoin at Stradey Park.
Llanelli Chief Executive Stuart Gallacher, who has led the campaign for the Scarlets to compete as a stand-alone club next season, is one of two Welsh representatives on the European Rugby Cup board.
"Under the terms of the Paris Accord, which was signed by all countries who play in the Heineken Cup, it is clear that any change would need the unanimous vote of the European Rugby Cup board," Blanco told 'The Times'.
"The French clubs would like to continue to play against club teams like Cardiff, Swansea and Llanelli."
The next meeting between Moffett and the Welsh club owners is scheduled for Tuesday, 14 January.
You can hear more about the issues on Scrum V, BBC Two Wales, Sunday, 12 January, 1920 GMT