National says Labour Party president Mike Williams has added weight to its claim that the party used taxpayers' money illegally during last year's election campaign.
Mr Williams said Labour's pledge card was an integrated part of the party's election campaign, and that party volunteers "assembled" it - fitting the credit card-sized card into slots on a cardboard pamphlet - before it was delivered throughout the country.
National says that is more proof that the card was an electioneering expense, and was unlawfully paid for with taxpayers' money from the parliamentary leader's budget.
Mr Williams made the admission while responding to other questions about the pledge card.
He was denying rumours of a dispute between the party organisation and the office of Prime Minister Helen Clark over who should pay, and that the party had rejected a request to foot the bill.
He said the party's budget for the campaign had been drafted in October 2004, and that that would have been the time any approach would have been made for the party to pay for the card.
"And that simply didn't happen. There was no clash of any sort.
"We had to integrate it [the pledge card] into our planning because a lot of it was assembled by party volunteers."
The card, which cost $446,000, is thought to be the largest item among taxpayer-financed advertising that the Auditor-General has provisionally deemed to be unlawful.
National MP Murray McCully said using party volunteers to assemble or distribute material officially dubbed as for "parliamentary purpose" was not against the rules, but "it lends weight to the fact that this was being used for a campaign purpose rather than for a bona fide parliamentary purpose".
"Campaign volunteers do not generally go out distributing bona fide parliamentary communications."
What made it "absolutely beyond dispute" that the card was an electioneering expense was that it was unveiled at Labour's campaign launch.
Asked why National had not objected so strongly to the fact that Labour had also charged the 2002 and 1999 pledge cards to the parliamentary leader's account, Mr McCully said the party did not find out until after last year's election.
"It never occurred to us in our wildest dreams that a political party would use the parliamentary leader's budget for what is so obviously Labour Party campaign expense."
Parliamentary Service general manager Joel George yesterday sent to Auditor-General Kevin Brady responses from parties identified as having unlawfully spent parliamentary money on election advertising in the three months before the election.