Attorney General Chris Finlayson has found that parts of the Government's welfare reforms are discriminatory.
In a report, Mr Finlayson says the legislation enabling the reforms breaches the Bill of Rights on the grounds of sex, marital status and family status.
The Attorney General says the bill is discriminatory because it introduces a work test to the Domestic Purposes Benefit but not the Widow's Benefit or the Women Alone Benefit.
The Labour Party's social development spokesperson, Annette King, says it is the most scathing report she has ever seen from an Attorney General.
She says the findings show just how ill-thought out the reforms are.
Social Development Minister Paula Bennett says she thinks it is a discrimination that most New Zealanders will see as fair and reasonable.
A men's rights advocate says the proposed work tests should be applied equally to men and women.
Widows and women over 50 on the benefit are exempt, but not widowers or men over 50 looking after children - which the Attorney General says breaches the Bill of Rights Act.
The Coalition of Fathers spokesperson, Jim Bagnall, says work test rules should be applied across the whole population.
"What we're looking is a continuation of discrediting men who've taken on that parental role."