The Libertarianz have said they are the only ones behind a private prosecution asking that the Labour Party pay back $800,000 of its 2005 election campaign spending.
The party's High Court action comes ahead of the Auditor-General's final report into the use of taxpayer money for political advertising.
A leaked draft report showed the Auditor-General's preliminary view was that much of the taxpayer-financed party advertising before last year's election was unlawful.
As much as $800,000 of Labour's spending is believed to be under question. This includes the $446,000 spent on the party's pledge card.
Prime Minister Helen Clark this morning questioned how the Libertarianz could afford the services of a high profile QC to take the claim to the High Court.
The Libertarianz'action names Labour MPs as first respondents and Parliamentary Services as second respondents.
Speaking on Newstalk ZB earlier today, the Prime Minister said it was "old news" that the "small right wing outfit" was taking the case.
But she asked how the Libertarianz had the money to pay for high profile Auckland QC Tony Molloy.
"I think the more interesting question is who funds all these attacks," she said.
"The pledge card was funded for the previous two elections without the auditor-general raising a single query.
"The National Party funded commitment leaflets as recently as the previous election without the auditor-general turning a hair. Now my question back is what has changed relevant to those publications."
However, Libertarianz leader Bernard Darnton insisted his party was paying for QC Tony Molloy to take the case and that his fee was reasonable.
He said the issue was one people had been quite upset about for some time, so the group had been asking for donations.
A statement on the party's website said: "Of course, the question is not how we have the money to hire QCs... The question is how the Prime Minister got the money to pay for her pledge cards."
- NEWSTALK ZB / NZPA