Former members of the Exclusive Brethren allege the secretive sect is breaking up families, putting members in isolation and attacking their livelihoods in order to maintain control.
Last week RNZ revealed the church, which gets millions of dollars in taxbreaks each year, is using private investigators and lawyers to fend off its critics.
A chance remark to her adult daughter three years ago triggered a chain of events that has left a Christchurch woman and her husband estranged from eight of their nine children, 25 grandchildren and wider family, and repeatedly hauled before the courts.
The couple, whom RNZ has agreed not to name, blame the organisation, which now calls itself the Plymouth Brethren Christian Church.
This faithful Brethren of more than 60 years said her family has been torn apart.
"At the moment, we just feel they have destroyed our family, and I don't see how the damage can ever be repaired."
Their ordeal started when the church's world leader, Sydney furniture salesman Bruce Hales, visited Christchurch and chastised a couple of local Brethren in front of a congregation of hundreds of people.
The woman told one of her older married daughters she felt sorry for them. That was reported back to the leadership and she and her husband were disciplined.
A few months later, they flew to Australia with their 14-year-old daughter to visit relatives, but were turned away on the orders of the Brethren leadership.
They had been "shut up", forbidden to communicate with anyone.
They came straight home without even seeing the woman's parents.
Her mother has since died.
Soon after that, their youngest daughter went to visit one of her older sisters and never came back.
When the father turned up at the house to bring her home, there was a confrontation.
He said he put his arms around her to lead her to the car, and his elder daughters and a son-in-law tried to prevent him. He was knocked over, still holding the girl.
"I was left on the ground with my glasses flung off and bruises on my arms. They had rung the police, and I got arrested for common assault."
After doing a non-violence course he was granted diversion, but was then served with a protection order.
He challenged that in court, it was thrown out, and the couple again tried to visit their daughter.
No-one would answer the door, but they were later both served with another protection order, claiming they had been violent towards their elder daughter, her husband and children.
They were both ordered to do a non-violence course but the facilitator referred them back to the court, which appointed a counsellor.
The counsellor tried to contact the family on their behalf, but was threatened with legal action.
After leaving a phone message for his elder daughter (apologising for any harm he may have unknowingly caused her), he was arrested three days later - at 1am - for breaching the protection order, and spent the night in the cells.
The mother was allowed to visit their youngest daughter on her 15th birthday.
"I said 'Can I bring her a present?' And I just saw her for about a minute. She gave me a hug and she was really pleased to see me and that. But she still said to me as I let her go 'You just get right, Mum'. I didn't say anything to her because I thought, the kid doesn't even know what she's talking about. It just gets drummed into her that that's the thing to say."
When they tried to contact her on her next birthday, they got a lawyer's letter warning them they were breaching the protection order.
Last August, they got a phone message to say they were finally "withdrawn from" (excommunicated) by the Brethren.
No-one from the church had contacted them in the 18 months prior to that, he said.
"And we don't know what we've got to get right about, I mean you've just got to grovel to get back, I don't know what you've got to do, I've never been in this situation before."
His wife said they had asked many times why were they "shut up" in the first place and why had they been withdrawn from. "And they can't tell us."
Of their nine children, they have contact with just one: Their 26-year-old daughter, who left the church when she was 18.
The Doctrine of Separation means godly Brethren must hold themselves apart from the sinful world.
This includes members of their own families who leave the church - or are thrown out.
Hales' word is law. His sermons are regularly published in "white papers" and distributed to 50,000 Brethren world-wide.
In 2015, Hales told a congregation it would be better for a man to drink rat poison than to have contact with an "opposer" - someone who had left the church.
That man was not named in the white paper, but it was widely understood he was referring to one man: Aucklander Braden Simmons, who had contacted his sister who had been excommunicated.
Simmons said that was the moment when he realised he could no longer believe in Hales, who is venerated by church members as "The Elect Vessel".
When Simmons started sharing his honest opinion with his fellow Brethren, he was "shut up then shut out".
He described it as "like landing on Mars" - but he counts himself fortunate compared with some ex-Brethren who have been cast adrift with no safety net.
"I did have a job and I did have a house, those are important things. There are some pretty nasty stories - it can leave people in a pretty vulnerable spot."
He was pressured to resign from the family business but refused.
They tried to break the company by making the other Brethren staff resign and banning members from doing business with them, but that did not work.
Then his father was ordered to fire him.
"I simply said: 'I'll go to the employment court, get damages and get my job back'. He couldn't fire me, and as a result he's been in solitary isolation for over a year now."
His father has not been excommunicated - but he is "shut up", cut off from both the Brethren and the world.
"They've increasingly taken quite literally to just putting people in confinement as a permanent holding bay, just getting rid of their problems that way. There's a number of people shut up in Auckland."
These people, like his father, still retain a hope of getting back into the Brethren, so they are quiet and careful to keep the rules.
Simmons has not gone quietly and is paying the price.
Last July, lawyers and private investigators arrived at his Māngere Bridge home before dawn to carry out a private search warrant of the house and all devices.
His former boss (a senior Brethren leader) has ongoing legal against against Simmons, alleging he has confidential information belonging to him.
Another ex-Brethren from Wellington, Rob McLean, was staying there and also had his laptop examined.
It is more than 10 years since he was excommunicated and lost his home, his family and his business.
He has had trespass notices and protection orders used against him.
"My biggest concern is the Brethren's exploitation of the legal system," he said.
"People are afraid to take them on because of the money they have at their disposal. Meaning they can silence pretty much anyone they want."
Simmons is now reconciled with his sister, Lindy Jacomb, who was 20 when her parents told her there was no longer a place for her under their roof.
She was "the opposer" identified by Hales as more deadly than rat poison.
"It's extreme language to choose but I refer to it as being like a suicide while you're still living, because it was like that for me. I realised, 'I'm going to have to say goodbye to everybody that I know'."
The Plymouth Brethren maintains it does not stop families from having contact with members who have left the church.
They declined an interview - but in a written response to questions, Brethren spokesperson Doug Watt said: "Just like any church, we are sad if someone leaves us, but wish them all of the best in their lives, and of course, hope that one day they will change their mind".
While they cannot comment on the actions of individual members, the church leadership had no knowledge or involvement in any of these matters involving private investigators, he said.
RNZ also asked whether Simmons was pressured to resign and the other Brethren staff told to resign, if other Brethren were banned from doing business with his firm and whether his father was told to fire him and "shut up" when he refused.
Watt said the church rejected the allegations and denied such actions were requested by the church or its leadership.
"Suggestions the Church would try to put someone out of business are completely untrue and entirely inconsistent with our values and faith."
However, in Jacomb's opinion, the idea that families were exercising "personal choice" in cutting off ex-members was merely "a public relations line".
"The Doctrine of Separation is undoubtedly a theology and a principle that is taught and maintained by the church and their leaders, whom they believe are the infallible manifestation of God.
"It's a complete myth to say it's the individual's choice.
"Yes, the individuals have chosen to practice that separation and enforce it. But they do so because their entire environment has conditioned them that outsiders are a threat, and family members who leave are a threat, and must be cut off - or their own eternal salvation is in question."
She never met her grandfather, who was shut out before she was born, along with a great uncle, and two aunts, one of whom was excluded after being raped.
The sudden death of Jacomb's close friend when she was 16 caused her to start asking questions about the basis for all the rules and prohibitions.
"I was constantly going to the leaders' ministry books, they call them, their writings from over the years and just wanting to understand 'If we can't wear necklaces or go to the movies, there must be good reasons, I'll just look it up and then I can understand'. I just had a desire to understand why we lived like we did. It never once entered my mind that we could be wrong."
Unable to find satisfying answers to her questions, she started reading the Bible - something Brethren are not encouraged to do.
While they go to church meetings every night and several times on Sunday, the focus is on the teachings of Hales.
However, scripture only made her more confused because it seemed to contradict how the Brethren lived.
"It's very clear that Jesus hung out with 'sinners', with people who were broken and didn't have it all together. Yet the Brethren are very focused on having it all together and if you show the least sign of brokeness or sin, you get booted out."
Jacomb was so terrified of having her doubts exposed that she kept her research in a locked briefcase.
Forbidden to use the internet, she started writing to a young man whom she knew was thinking of leaving the church.
Their covert correspondence was revealed accidentally when he wrote the wrong PO Box number on a letter and it ended up in the hands of a senior Brethren leader.
Cradling her newborn daughter in her arms, Lindy said she struggled to understand how her parents were able to disown her completely 13 years ago.
"The only thing that helps me to understand it is, there are circumstances in this world - and the Exclusive Brethren is one of them - where the crushing circumstances of the environment make parents decide to walk away from their children."
Wellington man Peter Hart is starting life again at the age of 52.
He was "withdrawn from" four weeks ago and has separated from his wife, five children and one grandchild.
In some ways, however, it was a relief to be able to speak his mind after years of trying to swallow his doubts, he said.
"My wife and I had a good relationship but we both knew there were certain things we couldn't talk about because things would go off the rails pretty quickly.
"You can't speak out, you can't speak your mind and it's a real strain because that's your whole life: the Brethren are your only friends, your only social life - it's very intense.
"People say to me, 'You lost so much, why did you do it?'. Maybe I made the wrong decision to speak out, but I did hold onto those thoughts for 17 years."
Hart said everyone was "terrified" of Hales, and he doubted anyone would do anything significant - like take legal action against an ex-member - without his blessing.
"It's not true to say they 'wish those who leave all the best': They tell you 'you will fall apart, suffer financially, won't keep faith, your health will fail, you won't have relationships'..
"You're not allowed to think for yourself. One saying in there is from the leadership: 'You do the doing, we'll do the thinking'."
Investigative journalist Nicky Hager has uncovered widespread use of private investigators by senior Brethren against ex-members in New Zealand.
"If we as a society can't protect people in that very vulnerable state, escape from something like a cult where their lives were being controlled and then they find themselves still being harassed, if we can't protect them, then something is really wrong."