Act's Mt Albert candidate, John Boscawen, says the National Party is begging him to go soft on Melissa Lee.
He has turned it down, saying Ms Lee lost all credibility she had left yesterday when she effectively conceded defeat in the seat even though there are still three weeks until the byelection on June 13.
Ms Lee told a radio interviewer she would come second - then tried to retract this later in the day.
Mr Boscawen said that left him the only centre-right candidate in the running, and urged National supporters not to waste their vote on Ms Lee.
Mr Boscawen said a National Party figure he refused to name "pulled him aside" earlier in the week and said "you can't attack our candidate, we won't attack you".
Mr Boscawen said he could not accommodate this as all bets were off in a byelection and Ms Lee's performance meant he was the only credible candidate for right-wing voters.
Members of her campaign team again tried to get him to go easy on Ms Lee when he bumped into her in Kingsland yesterday.
Mr Boscawen said National "must be tearing its hair out" for choosing Ms Lee over grassroots toiler Ravi Musuku, who campaigned strongly against Helen Clark in Mt Albert in the past two elections.
Mr Musuku said he was surprised to hear Ms Lee had given up. Asked if he would have given up, he replied: "Never".
On National Radio's Morning Report yesterday, Ms Lee was asked if she thought she could come second.
She replied: "I am hoping to. It would be really fantastic if I nudge in a little further as well but I am not expecting to win.
"It was always going to be a hard battle."
Asked directly if she expected to come second she answered: "Yes".
Ms Lee later said she meant "I am expecting to come second, at least.
"I am not putting in all these hours and putting up with media trying to come second, I am not.
"I am trying to win this damn thing."