He denied the policy was unfair to males, saying although the list did allow the party to address under-representation, the party did not want to get into a situation in which most list candidates were female because there were too many male electorate MPs.
Asked whether candidate selections should be merit-based, he said the reality was that in most selections there was more than one nominee who was capable of being an MP.
"You have to make sure other factors which are not unreasonable enter it."
He said it was up to individual electorates to decide whether to make use of the new rule, should it pass. "If an LEC thinks it might be appropriate for their electorate, they can ask us if it's okay. If it is clearly being done solely to block somebody they don't want, then the Council can say no."
He said the UK had gone further to get the same result. He said the current Labour caucus would almost be at 45 per cent after the election of Meka Whaitiri in Ikaroa-Rawhiti "and we have to make sure we don't slide from where we are".
Green Party co-leader Metiria Turei said the new rule would make sure that women are able to put their skills forward on an equal basis to men.
"By having rules that allow women equal access to the process mean the women are definitely in the race.''
The Greens have a requirement that electorate branches consider gender equity when making candidate selection.
Act leader John Banks criticised Labour's move.
Mr Banks said when he entered Parliament in 1981 prior to the election there were four female members of Parliament, after the election there were eight.
"Today there are 40 women members of Parliament and I would like to see the day come when there's more women members of Parliament, and there's plenty of high quality women, on merit, that can get themselves into the Parliament without that kind of gerrymandering,'' he said.
Key proposals:
* Set targets of at least 45% of caucus members after the 2014 general election being women, and 50% after the 2017 election. Currently the caucus contains 19 men and 15 women.
* Mandate the moderating committee, which decides Labour's list after regional consultation, to make decisions which are in line with that target, following electorate selections.
* Establish as a pilot for the 2014 list creation process a Te Kaunihera Maori (Labour Maori) list conference working in parallel to the existing six regional list conferences.