The Family First lobby group has published an open letter to the Prime Minister citing evidence of families being prosecuted and children removed under the child discipline law.
National director Bob McCoskrie says a promise by John Key to change the law if good parents are criminalised should now be acted on.
The advertisement appears in two Sunday papers. It lists four cases which the lobby group says shows evidence of what it calls the "anti-smacking law" in action.
One example tells of two parents separated from their children for two nights. They were interviewed for five hours by police after admitting they sometimes smack their children.
A law change in 2007 removed the defence of "reasonable force" for adults accused of assaulting a child.
Mr McCoskrie says Mr Key needs to follow-up on his previous promise to make changes if the law harmed good parents.
He says a Royal Commission should also be established to tackle the real causes of child abuse.
Mr McCoskrie says changing the law now could prevent what he calls "a costly and time consuming" referendum on the issue, which is due to take place later this year.
