ACT's Epsom candidate, John Banks, says split voting by centre-right supporters in the electorate could be crucial to the election outcome.
Mr Banks is hoping voters will again back an ACT candidate, while giving their party vote to National.
He has told voters at a candidate meeting in Mt Eden that they should continue the Epsom custom of split voting, as National candidate Paul Goldsmith is high enough on the list to get in anyway.
"It's absolutely critical," Mr Banks says, "if you add up the numbers on the left and have a look at the polling right now, that on election night the call could be finely divided."
Two opinion surveys have shown Mr Banks trailing Mr Goldsmith in the electorate race, suggesting strategic voting may be less certain this time.
Mr Goldsmith says there is little he can do to ensure electors split their two votes.
"You can't tell people what to do. They'll make a judgement as the election comes closer. We're focussing on the party vote primarily, and it's up to the voters of Epsom."
The other candidates standing in Epsom are Labour's David Parker, the Green Party's David Hay and Mana Party candidate Pat O'Dea.