A win would give them a home final at Dunedin. But a loss to Tasman would cut them out of the final.
The other team in the equation is Southland.
When the Whalers beat Tasman by 20 points last year, centre Callum Smith scored three tries.
But he is playing for Tasman today and the Whalers defence will need to nail him to win the game.
Smith is one of the leading try-scorers in the South Island league this year and he will be keen continue his form against his old province.
The Whalers showed encouraging form in their first game of the season, beating the West Coast Chargers 62-18 in Dunedin two weeks ago.
A key player for the Whalers will be hard-running prop Jermaine Stone, who scored three tries against against the Chargers.
Others likely to feature are fullback Jonnie Hughes, halfback Sam Davison and hard-tackling Jury Arthur.
The goal kicking of Ben McKerchar will be vital.
He landed nine conversions against the Chargers.
