Super League and the RFL have condemned the ugly scenes in Perpignan at the end of the game between Catalans and Warrington.
The game, won 30-10 by the hosts, was overshadowed by the incidents in the crowd, which appeared to show fans fighting and items being thrown.
In a joint statement, they said: “We were appalled to see the pictures from Perpignan, and an investigation will be launched.
“The scenes are alien to Super League and have no place in our game. We will be taking firm action to make it clear this behaviour is totally unacceptable.”
It occurred following a fiery encounter that saw four yellow cards and two red.
Warrington have already issued a statement of their own in response to the trouble.