National deputy leader Gerry Brownlee has launched a stinging counter-attack against Act, saying it has "abused" its opportunities in Parliament over the past nine years and does not deserve to be returned at the election.
Mr Brownlee accused Act of employing "voodoo mathematics" to persuade National voters to split their vote and give the party vote to Act.
And he said National had no intention of either stepping aside or encouraging split voting in any electorate to save Act.
Mr Brownlee's outburst was in response to a description by Act MP Deborah Coddington of National MP Maurice Williamson as a "useless" Transport Minister.
Until now, National has bit its collective tongue over Act's new aggressive "break-out" attempt to destroy the perception that it is an appendage of National.
With less than seven months to go to the election, Act is struggling to poll more than 2 per cent.
Act MPs have criticised National counterparts and have even worked with the Government in question-time to allow it to criticise National for its early support of Te Wananga o Aotearoa.
Mr Brownlee told the Herald last night the attacks were "pretty shallow and will only ensure that they face oblivion at the election".
"It's the on-going determination by Act to keep alive by trying to suck breath off us, essentially.
"They came in [to Parliament] saying they were the most talented bunch of MPs ... the most creative, the most visionary, with the best ideas for improving New Zealand. What is one idea they have managed to advance in the last nine years? There isn't one."
Mr Brownlee believed that this election would not feature the vote-splitting of past polls.
"Act know that. Act spend more time agonising over polls than any other party."
The "voodoo mathematics" that Act had used in the past three elections were wrong and people realised that, he said.
"They have abused the opportunity they have had over the past nine years and they don't deserve to be back in Parliament."
Mr Brownlee last let rip at Act in 2003, calling them a smorgasbord of politicians with a superiority complex over the National Party.
Act has decided to give former Auckland mayor John Banks a high billing at its annual conference in Auckland at the weekend, contrary to earlier plans.
No announcement on his candidacy is expected for some time but it is thought the former National minister will stand for the party.
Act had decided several weeks ago to give Mr Banks no platform at the conference in order to minimise distractions from the profile of party leader Rodney Hide.
But that has changed, with president Catherine Judd saying it was a "flexible" programme.
She confirmed Act had been trying to secure California Governor Arnold Schwarzenegger to speak via video, and Mr Banks was a replacement for him.