Former Conservative Party leader Colin Craig is being sued for $1 million.
His former colleague and now bitter foe John Stringer filed defamation papers in the High Court at Auckland on Thursday.
Mr Craig launched a $750,000 defamation case against Mr Stringer in June.
Mr Stringer, a former interim chairman of the party's board, is claiming he was defamed in a pamphlet Mr Craig issued in July titled Dirty Politics and Hidden Agendas.
Mr Craig claims Mr Stringer defamed him on 31 separate occasions.
They both vigorously deny the allegations.
Mr Stringer said on Thursday he had repeatedly sought reconciliation or an apology from Mr Craig.
He's now received a formal refusal to apologise.
Their problems go back to the chaotic collapse of the party's executive and board in June this year.
Mr Craig resigned amid allegations of inappropriate behaviour and appears to be trying to make a comeback.
Mr Stringer announced he was interim chairman of the board after all the others quit, but subsequently resigned the position.
He says he's considering standing for the leadership.
Mr Craig led the party in the 2014 election campaign.
It won 3.9 percent of the party vote, not enough to get MPs into Parliament.