Ending solo mum sanction could cost govt $25m a yearby Craig McCulloch
Officials warn the cost could balloon if the policy is ditched.
Single parents who refuse to name the other parent have $22 deducted from their benefit every week per child. After 13 weeks, another $6 per family is docked.
The policy was introduced in 1990 to ensure fathers paid child support.
The Labour-led government last year confirmed it would repeal the penalty, saying there was no evidence it worked.
A Ministry of Social Development report - obtained under the Official Information Act - said the government would pay out at least $25 million more a year as a result of ditching the sanction.
Officials warned that cost could balloon, "potentially considerably", if people were then incentivised to rip off the system.
For example, mothers might choose not to name the father so he could avoid paying child support to the Crown and could instead pay her privately under the table.
Acting Minister of Social Development Peeni Henare said the current penalty unfairly punished thousands of children in low-income families.
"We do not believe children in these households should have to foot the bill and be unfairly punished for an absent parent."
He said the $100m figure was an early estimate and the final cost was still being established.
"And while it is a cost and we acknowledge that - it's actually the cost of ensuring sole parents are given their full entitlement."
However, National's social development spokesperson Louise Upston said the report showed the government's policy had a "dark side".
"Vulnerable women will be threatened with all sorts of things not to name the father.
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