The Social Workers Registration Board has renewed calls for mandatory registration for social workers.
Its chair Shayne Walker told Parliament's Social Services Select Committee today that up to 6000 unregistered social workers could be working with some of the country's most vulnerable people, including young children.
He said all workers should be regulated to keep the public safe.
Mr Walker said it would be no different to having a registered nurse on a hospital ward.
He said the board could only investigate complaints made about a registered social worker.