Two of New Zealand First's biggest backers say their members' support will be lost if the party helps pass the Electoral Finance Bill.
The Sensible Sentencing Trust yesterday said it would withdraw its vote for the party at the next election, describing NZ First leader Winston Peters as having lost the plot.
Grey Power, meanwhile, indicated that NZ First loyalists within the group could turn away from the party next year.
Heads of both organisations are involved in a four-party application for a judicial review into the bill, arguing that the bill's wide definitions of third parties and advertising would limit their advocacy activities, and would be in breach of the Bill of Rights Act.
But Mr Peters said they were misinformed. As he spoke on the bill in Parliament on Tuesday, he challenged opposition MPs to name one person who would not be able to speak freely next year.
An interjector said Garth McVicar - national spokesman for the Sensible Sentencing Trust - and Mr Peters responded that [law and order spokesman] Ron Mark and he had worked closely with Mr McVicar for many years and would continue to do so.
But Mr McVicar said yesterday: "Our stance will certainly be that we don't see much point in supporting NZ First any further. I would imagine we've got thousands more members than [NZ First] have throughout New Zealand, so I think they're dead in the water, realistically. I think Winston's just totally lost the plot."
Grey Power national vice-president Don Chapman said the organisation was apolitical but he would not be surprised if NZ First loyalists within the organisation's 95,000 members turned away from the party too.
"I would be very, very surprised if [Mr Peters] was supported, because we are very anti that bill, and the implications that the bill would have on us as an organisation."