The Christian lobby group Family First has lost the right to appeal a decision that stripped them of their charity title.
In a decision released on Tuesday morning, the Supreme Court said it has allowed the Attorney-General's appeal against a Court of Appeal decision in 2020 that meant Family First could be a certified charity.
That means the 2020 decision has been overturned by the Supreme Court and Family First no longer qualifies for charitable registration.
Family First's purpose "crossed the line between education and advocacy", the Supreme Court said.
In 2020, the Court of Appeal set aside a decision by the Charities Registration Board - meaning Family First could again qualify as a charity.
The Attorney-General was subsequently granted leave to appeal that decision by the Supreme Court after being called upon by the registration board.
In its decision, the Supreme Court said Family First's research lacked the balance "required to further an educative purpose".
"One-sided promotion of personally held views detracts from the cohesiveness of our pluralistic society and disempowers the receiver by failing fairly to inform them of alternative viewpoints on the subject. Family First's promotion is self-referential; it is not about community.
"Honesty and respect in debate is not self-referential. But Family First's advocacy is not fair, balanced or respectful, so its advocacy is not charitable."
Family First chief executive Bob McCoskrie said it was a "sad day for the freedom of speech and belief in New Zealand".
"The attempt - some would label it a 'witch hunt' - by the Charities Board to deregister Family First is a watershed decision, not just for Family First, but for the whole country," he said in response to the Supreme Court ruling. "The good news is that Family First will not be silenced and will continue to represent and be a powerful voice, and advocate for the thousands of families who support us."