The National Foundation for the Deaf is urging the Ministry of Health to urgently follow up on cases where babies have been given faulty hearing screening tests.
Letters have been sent to the families of about 2000 babies recalling them for tests after the ministry discovered irregularities in its newborn hearing screening programme.
Foundation chairman Peter Thorne says recall letters are often ignored.
He says without screening it can take up to four years for a child to be diagnosed with a serious hearing impairment.
"That's far too late, because the language centres have sort of closed off by that time and you can't put in interventions which are very effective."
He says the purpose of the screening programme is to find babies with hearing impairment in time so their language develops properly.
Professor Thorne says screening failure is an inevitable consequence of underfunding and
the foundation has raised concerns about inadequate monitoring and data collection.