In Auckland alone this number totals over 5000 parents and almost 7000 sanctions.
Women are disproportionately affected making up 98 per cent of cases.
Stephanie said it was like the Government was punishing her and her children, when the blame sat with the fathers.
Instead it was her and her babies that went without food and clothing and struggled to make ends meet.
"Caring for them isn't hard, but financially it is. We can't afford heaps of things.
"[Work and Income] expect us to better ourselves but then put us in this predicament. This sanction is hanging over my head."
Green Party co-leader Metiria Turei called Section 70A a misogynistic piece of legislation that needed to be scrapped. She said it caused enormous harm to New Zealand's poorest families and meant they lost up to $200 a week from their already meagre income.
"These women who are in need of financial support from the state do not deserve to be interrogated and harassed by Winz about a very personal decision they made for their child's well-being."
Turei had felt the sting of the sanction herself when she didn't name the father of her daughter. She said she did it to protect him from Winz harassment with the goal to keep their relationship positive for their daughter.
Other reasons could include the child resulting from a rape or the woman was worried about the father exerting legal rights over the child, particularly if the relationship had been violent, Turei said.
"The reasons why women do not name the father are complex and personal."
Auckland Action Against Poverty spokeswoman Vanessa Cole called the policy sexist and racist. Over 50 per cent of the penalised parents were Maori.
Cole said it had been established with the aim to get more fathers to pay child support. But it backfired and instead only economically punished solo mums and their children.
"It's such an old school policy that needs to be removed completely," Cole told the Herald.
A Ministry of Social Development spokeswoman said the policy was introduced in 1990 to encourage the other parent to take responsibility and contribute to the cost of raising their child.
"If a person does not apply for Child Support or identify the other paying parent, their benefit rate will be reduced."
The spokeswoman said an exemption can be granted for reasons such as family violence concerns, the pregnancy being a result of sexual violation and insufficient evidence being available to establish who the other parent is.
But Cole said an exemption was difficult to obtain and meant the beneficiary had to disclose their sexual history to a lawyer and then retell that story in an open-plan Winz office.
