It's set to be Tauranga's biggest game of rugby in four years and, for one shadowy group of Steamers supporters, the warm-ups have already started.

The Bay of Plenty Mafia - the Steamers' most official unofficial supporters - are counting down the hours until they can resurface to cheer their team on against Southland at Baypark Stadium tomorrow night.

"They're definitely gonna do it," said die-hard Steamers supporter and Mafia member Honki. "Playing at home - it's the crowd advantage."

Honki, who would not reveal his real name, has barely missed a Steamers match this season.

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Between him and the rest of his cronies, there has been a banner wielding, blue and yellow body painted bellowing Mafia member at every North Island match during the Air New Zealand Cup.

"We all have a love and passion for the Bay of Plenty team, irrespective of whether we're getting spanked or whether we're doing well. And we take our kids along.

"It's not just for the adults. Our children get all dressed up, and now I'm starting to drag the nephews along too. My partner dresses up exactly the same. We both tend to lose our voices by the end of the game."

Honki thinks the Mafia's unwavering support has infiltrated into the general public.

"That's probably one of the biggest things I've enjoyed in this year's games. Friday nights at Baypark, we've been getting 8000-10,000 people. We haven't seen those crowds since 2004.

"With the radio saying 'expect a crowd of 10,000', I'll be disappointed if it's not 15,000."

Not even last week's thumping by the Magpies could cut down the legs of the pedestal on which the Steamers have been placed.

Just look at last week's entry on the homepage of the Mafia's website: "Apparently we deliberately lost a game on Friday night having worked out we wanted to play Southland in the quarter-finals. Well done boys."

Honki agreed, it was a good "strategic" move, as was the Northland win over Auckland. "I think we need to post a cheque to Northland rugby for that because, if they hadn't beaten Auckland the way they did, we would be playing Auckland at home."

But money doesn't solve everything and even the Bay of Plenty Mafia know that. "We need to make sure our boys turn up for the second half, because that's their Achilles heel for the whole season. We play a brilliant first half and then we've tried to hang on in the second."

So that will rest in the hands of the Steamers, but there's one thing the Mafia can do, and that's to encourage a crowd worthy of a quarterfinal.

Honki's message: "Turn out and en masse ... and bring your voices."