Canberra Region Rugby League have been investigating the incident, where male spectators allegedly shouted racist slurs like "dirty black dogs" from the sideline of the game between the WorHawks and the Raiders at Harden on July 31.

While the spectators were allegedly asked to stop, they weren't asked to leave.

CRRL general manager Mark Vergano said the match review committee had proposed a sanction for Harden, with the Riverina club having until Monday to respond.

If they choose to contest it then a formal judicial process would begin - which would usually be held within a day or two of the response date.

Vergano declined to say what the sanction was only that they'd proposed one.

Harden didn't return The Canberra Times' calls.

"It's ongoing. The match review committee's has put an initial judgement to Harden and they're considering it," Vergano said.

"That's about all I can say at the moment because it's got to go through the process now."

NRL Indigenous stars Jack Wighton and Latrell Mitchell threw their support behind Boomanulla by sharing posts of the incident on social media.

Boomanulla player Beth Cooper told The Canberra Times they had taken the matter to the league to try to ensure incidents like this didn't happen again in the future.

She said having high-profile players like Wighton show their support helped raise awareness of the problems Indigenous players faced.

"Every Aboriginal person can resonate with it. Growing up you're told to keep your head down, don't rock the boat ... but these behaviours are unacceptable and shouldn't ever be allowed to continue," Cooper said.

"It has been a really good response. It began as something that was really negative to ... having people be so outraged, we're already outraged, but just to have people in the community also back us up is empowering."