The Ministry of Justice has told MPs a blanket approach to stopping convicted child sex offenders legally changing their names would not work.
The ministry has appeared before a parliamentary committee to give its view on how such a law would work in practice, as contained in the National MP Jian Yang's member's bill.
Policy advisor Pasan Jayasinghe told MPs the bill would hinder offenders' rehabilitation and reintegration.
And he said sex offenders could easily get around the policy.
"You don't need to register a name change to use a new name, a new name comes into affect just by the simple fact of using, registered name changes are only required for very specific statutory requirements, for example a passport."
Mr Jayasinghe said the sex offenders' register, which the government was in the process of establishing, would be more effective.