Family First is set to lose its charitable status, the Herald has exclusively learned.
The group was first notified by the Charities Registration Board in 2013 that its charitable status was in danger.
That was because the group advocated a controversial point of view, that was seen as lobbying for a political purpose.
The decision was challenged in court, and in 2015 the High Court ordered the Board to reconsider its decision.
The High Court decision did not rule on whether or not Family First was a charity.
The Herald understands that decision has now been reconsidered, and that the formal notification process is underway to tell Family First it is being deregistered as a charity.
Deregistration means that they cannot claim tax exemptions for their donations, and usually means the Inland Revenue Department will no longer allow donors to claim tax rebates for donating money to them.
A Department of Internal Affairs spokesperson said the department couldn't confirm or deny the deregistration before speaking with Family First.
However, in a statement, the spokesperson said Family First would remain a registered charity while any court action was underway.
"We can't make any comment while this process is underway but a final decision will be made by the independent Charities Registration Board.
"The Board's reasons for its final decision will be publically available."
Family First national director Bob McCoskrie said they'd be going straight to their legal team and instructing them to take the matter back to court.
"It may go as high as Supreme Court, because we're not going to lie down on this one.
"It should be disturbing to all New Zealanders that a charity that researches and speaks up on an issue, which is deemed incorrect by the political elite, is in danger of being penalised.
"I'm sure there'll be some people celebrating the fact that Family First is going to be deregistered.
"My warning to them is that one day a Government that disagrees with their view may come gunning for them."
McCoskrie said lobbying was part of their work, and didn't stop them from also being a charity.
"We're charitable because we don't make a profit. We rely purely on donations.
"The problem is the Charities Board is not being consistent, because if it was, there'd be a whole lot of other groups that should be panicking."
McCoskrie said they were fighting the decision on principle, as being deregistered as a charity wouldn't stop their work.
He said people who donated wouldn't stop donating purely because the tax rebate was cancelled.
The 2015 High Court Family First judgment is online here.
Greenpeace has previously fought through the courts to remain a registered charity.
The Supreme Court decided in 2014 that they were allowed charitable status, after the organisation was previously dismissed for being too political and staging protests that were illegal.