The Children's Commissioner is warning that money-saving measures will result in the need for a second Royal Commission into abuse in care.
Ministers removed the current inquiry's ability to investigate modern cases of abuse in April to save both cash and time.
Andrew Becroft has now written to the government and urged it to re-instate the inquiry's power to investigate incidences of abuse since 2000.
He is warning the government will be handed an incomplete report if this doesn't happen.
In his letter, Becroft points to a recent video published by Newsroom that shows a young person being tackled, restrained and held in a headlock by Oranga Tamariki staff at a care and protection unit in Christchurch.
An investigation has since been launched, staff at the facility have been stood down and the residence will be temporarily closed.
"We still hear regularly of children in state care talking about abuse. It's a live and an ongoing issue and we don't want the job only three-quarters done," Becroft said.
Internal Affairs Minister Jan Tinetti insisted the inquiry has the discretion to look at modern cases, just not investigate them.
"There's been quite a bit of confusion about that. What we have removed is their ability to look at a systemic investigation; so going into each current care setting and having a systemic investigation. They can still hear from individuals, and they still are, and they can still make recommendations about current care settings."
The Royal Commission estimates up to 57,000 children and adults have been abused in care since 1999.
Becroft expected some of those people will believe their experiences don't matter because of the government's decision.
"I think it's all too easy for us as adults to sort of say historic allegations are more significant. Actually we all stand condemned I think, me included, if we don't commit ourselves to hearing now what's also going on. I think that's so crucial."
If the government refuses to reverse its decision, Becroft feared another Royal Commission would be needed in future to investigate the abuse experienced over the last 21 years.
Sonja Cooper, a lawyer representing more than a thousand abuse survivors, shared the same fear.
"It is cutting it off at its knees and, of course, there will be calls for another Royal Commission to be set up to do the job of looking at what's going on now and what needs to be done. It's already clear from those of us that work in this area that actually their current model is a complete and utter failure."
Tinetti said the Government will not reverse the changes.
"The Royal Commission has always been for the historic abuse in state care and faith-based institutions from 1950 to 1999. This is not the vehicle for current care setting and to investigate the current care settings."
There are reviews into modern care providers underway and anyone wanting to make a complaint about the treatment of a child or person in care can contact the Children's Commissioner, the Ombudsman or the police, she said.
Commission chair Judge Coral Shaw said: "The Royal Commission can also consider contemporary issues and experiences so that recommendations can be made to avoid future abuse."
The Royal Commission said it welcomed public discussion on how abuse can be prevented now and in the future and remained committed to revealing the extent of historical abuse.