Mourad Boudjellal has warned Warren Gatland that Toulon would require a fee to release Rhys Webb from his contract.
Webb is the major casualty from the Welsh Rugby Union's (WRU) new policy on overseas-based players that was announced in Cardiff Monday.
Under the policy -- which takes effect immediately -- only players with at least 60 caps, or who started a contract before the rule came in, would be considered for the national team if they ply their trade outside of Wales.
Gatland has expressed his unease at the situation, given Webb falls 32 caps short of the threshold, and suggested the scrum-half should reconsider the move.
However, Toulon owner Boudjellal insists he has a binding agreement with the player.
"I have a signed contract with Webb," Boudjellal told L'Equipe. "If Warren Gatland wants to pay the release clause, no problem.
"But if Gatland pays, it will require a certified cheque. I've not heard from either Webb or his agent [Monday] but it does not change anything for us. I am very calm."
Webb's move to the south of France on a three-year contract was confirmed earlier this month.
The 28-year-old insists he was not made aware of the impending change in policy before he agreed to join Toulon.
Under the WRU's previous selection policy, Gatland would have been allowed four wildcard picks during the 2018-19 season meaning Webb's international career could have continued.
"I didn't know the full implications when I agreed to join Toulon because the change in the selection policy came out after I signed," Webb told WalesOnline.