Mr Ansell, who lives in the Wairarapa, says the billboards are a form of attack politics but the backlash from Nicky Hager's Dirty Politics book had not made backers reconsider running them.
"All round the world people say that attack advertising is horrible, and all around the world it works," Mr Ansell said.
"These are valid criticisms in a political system, not dirty politics."
Information distributed by the Opinion Partnership says it is concerned about the influence the Green Party would have in a Labour-led coalition government.
Mr Ansell is one of three publicly declared members of the group. The other two are former Federated Farmers president Owen Jennings and businessman John Third, of Johnsonville.
Mr Ansell says the campaign targets two types of voters, male blue collar workers who traditionally vote Labour and upper-middle class women who care about the environment.
In contrast to Mr Ansell's comments, Mr Third says he does not think the billboards are a form of attack politics.
"Our objective is not attack politics, our objective is actually to stimulate some proper analysis of policy."
Mr Third refused to answer questions about who was funding the Opinion Partnership and how much they were going to spend campaigning.
Under the 1993 Electoral Act third party promoters must register if they spend more than $12,300 on their campaign. Wairarapa Times Age