Under current legislation individuals can adopt regardless of their sexual orientation, but the 1955 Adoption Act makes no provision for same-sex couples.
"It's an obscure and archaic provision in our law," said Turei.
"We haven't properly addressed the straight-out prejudice that law supports and kind of perpetuates."
Last month, the New South Wales government announced a review of its adoption laws, putting it in line to become the fourth Australian state to legalise same-sex adoption.
In 2002, Labour promised to reform the Adoption Act after Law Commission and select committee reports on the issue. But it is not mentioned in last year's Law and Order policy and is not on the government's work plan.
Turei believes Labour has pulled back on adoption reform because of its relationship with more conservative parties such as New Zealand First and United Future which do not support its "pink think" polices.
"Labour's agenda this term will be much more conservative because of their choice of coalition partners and it's incredibly disappointing that some of the strong principles they've taken in the past will go by the wayside."
Justice Minister Mark Burton agreed there was a need for adoption reform, but said opportunities to advance it were limited by the support available under an MMP parliament.
He said Labour had removed much legal discrimination against gay and lesbian people, including passing civil union laws and the Care of Children Act - which addressed some of the issues faced by same-sex couples who have or want children.
Under the Act, a birth mother can list her female partner as a parent on the baby's birth certificate and the partner can apply for guardianship -giving the couple all legal rights and responsibilities for the child. But the only options for gay male couples wanting to adopt are for one of the partners to adopt, both to apply for guardianship, or through a surrogacy arrangement.
Gay and lesbian people who spoke to the Sunday Star-Times said the adoption law was discriminatory and often hit gay men the hardest.
"One of the silent griefs that many gay men have is that they will not be fathers," said Neville Creighton, co-ordinator of the Auckland Gay and Lesbian Welfare Group.
Canterbury University senior law lecturer John Caldwell said many people saw the 1955 Adoption Act as antiquated.
"In terms of the modern family suite of statutes it's a real anachronism. The age says it all but remarkably parliament's not touching it."
Same-sex couples can foster children and many gay couples have children through past relationships.
New Zealand First family issues spokeswoman Barbara Stewart said her party believed traditional New Zealand families provided a suitable pool of prospective adoptive parents.
"Given that the demand exceeds the supply, New Zealand First remains opposed to gay adoptions."
The Catholic Church's communications director Lindsay Freer said the church would oppose any reform allowing same-sex couples to adopt.