The Brumbies are attempting to rally rugby supporters in the capital to boost attendance numbers for the next home match against the Japan Sunwolves on June 3.

The Brumbies will donate $15,000 to three charities as part of a '15 for 15' program in the hope of tripling crowd numbers from 5000 to 15,000 next week.

Chief executive Michael Thomson and chairman Phil Thomson sent an email detailing the plan and warning the "Brumbies may no longer exist" if crowds don't go back to Canberra Stadium.

"We know you want rugby to thrive in this region and, in part, to achieve this, we need a successful side playing in front of big crowds," the letter said.

"This is important for at least three reasons, first we know the players perform better in front of large supporting crowds.

"Secondly because the funds attendance at games generates enables us to invest back into our programs including community rugby, women’s rugby and our pathways, and without your support and those funds the Brumbies may no longer exist.

"And finally a successful team encourages people of all ages and all backgrounds to become involved in rugby and enjoy all the great things the game has to offer."

The Brumbies avoided the Super Rugby axe last year after Rugby Australia deemed the club an important part of the game's future given it was an original Super 12 franchise and Australia's most successful team.

But the damage of the ugly culling process, a confusing competition and a lack of interest in visiting teams has hit the Brumbies hard.

The Brumbies are in danger of recording their worst average crowd figures in the club's 22-year history if there isn't a spike in interest at their last two home games of the regular season.

The average attendance dropped to 8464 after just 5283 fans turned up to their last home game on a cold and wet night on May 12.

It means their average attendance is now below the previous lowest average of 8971 per game in 1997.

The team's results (they've won just three of 11 games), waning interest in the Super Rugby format and Australian rugby's woes have been the major contributors to the disappointing Brumbies crowds.

Crowd numbers are down at most Super Rugby franchises in Australia, New Zealand and South Africa.

But cross-code rivals the Canberra Raiders are proof you can re-engage with your fan base and turn dismal crowds into fanatical support.

The Raiders attracted just 6717 to their last home game of the NRL season in 2015. That number jumped to 18,825 for the last game of the regular season in 2016 and a total of almost 50,000 for two finals games.

However, the Raiders' average numbers are also down this year by more than 2000 per game as they try to get their season back on track.

"On Sunday [June 3] we ask that you come out as a show of support for your team, your city and your region and three charities which make a real difference to our community and ask friends and family to do the same," the Brumbies' letter said.

"...We recognise we are a work in progress with much to do and want to thank you for being part of the Brumbies family, your support is vital to us, and the game."

The Brumbies are hoping a more friendly 4pm timeslot will encourage fans to attend the match. The club will donate $15,000 to OzHarvest, Lifeline Canberra and Give me five for kids if they reach their crowd target.

SUPER RUGBY ROUND 15

Saturday: Pretoria Bulls v ACT Brumbies at Loftus Versfeld, 11.05pm. TV time: Live on Fox Sports.

SUPER RUGBY ROUND 16

June 3: ACT Brumbies v Japan Sunwolves at Canberra Stadium, 4.05pm. Tickets available from Ticketek. Fans will be allowed on to the field after the game.