A Victim Support worker joked about hitting his children during a talk at Destiny Church.
The worker was filmed making the comments at a Sunday gathering in late February.
In the video, he tells the congregation, who can be heard laughing on the recording, about smacking his kids.
"Some of you have heard my story. I had a cane, I had a long cane. When the law says don't smack your kids well, I broke the law.
"I had a cane. Bend over, whack! The other son comes. Bend over, bend over, stop lifting your head, whack!"
He then goes on to joke about smacking one of his children more for resisting punishment.
"Okay, you're going to get another one. Up and down, whack! Whack! You got three, son, because you kept going up and down. You're like a yo-yo!"
Independent victim advocate Ruth Money said the video was "absolutely shocking".
"It's an elder of Destiny Church bragging about harming his children. It's illegal to hit your children," Money said.
She said it would be bad enough if the person concerned was a volunteer liaising with vulnerable people, but for a person working in an organisation that is supposed to helping the vulnerable it was "absolutely disgusting".
When approached by RNZ, Victim Support said it was recently made aware of the video and was investigating.
"Victim Support does not condone the statements in the video," chief executive James McCulloch said in a statement.
"We strive to support and empower victims, including victims of physical violence, and it is essential that all our team uphold our values."
Money said it was hoped an independent investigation, its findings still secret, two years ago had improved systems at the taxpayer-funded charity.
"We've been down this path before with Victim Support for many years. Victims and the staff at Victim Support deserve a lot better."
Destiny Church referred RNZ to the man, who said he would not be making any comment as the situation was in the hands of his employer and under investigation.