Proposed changes to the child support scheme will cost taxpayers $91 million to implement, opponents say.
The Child Support Amendment Bill was reported back to Parliament from a select committee yesterday.
It aims to introduce a new formula for calculating child support payments where parents have separated.
The new formula takes into account shared care arrangements, the income of both parents and the decreasing expenditure for raising a child as it gets older.
Revenue Minister Peter Dunne introduced the changes because the assumptions of the current scheme were outdated and were based on the idea that the paying parent was the sole income earner.
The Green Party said the new formula was complex, unfair and not transparent.
''The costs of administering the new system, estimated by officials to be approximately $91million, are substantial, and we are not convinced that these costs can be justified for the introduction of a flawed formula that does not maximise child well-being.''
Several submitters said the amendment should explicitly promote the well-being of children as a core function of the law.
The bill also ignored a suggestion from Children's Commissioner Russell Wills that the Crown pass on payments received by the former partners of beneficiaries.
Currently that money goes to the Government to offset welfare payments.
''The money paid by the liable parents does not directly benefit the child in any way,'' the Greens said in their minority report accompanying the bill.
Labour was also critical of the bill saying it was a ''lost opportunity''.
''The overall effect of this bill is to apportion a greater share of the cost of child-rearing to women. Many women would be worse off as a result of this legislation," said Labour.
NZ First was also concerned about the bill because off the highly complex formula determining what was shared care and the assumption that there was a set cost for raising a child based on age.
The bill is unlikely to be back in Parliament before the summer recess.