National says the Labour Party's proposed quota system for women in Parliament undermines women's ability to succeed on merit alone.
Labour is considering banning men from running for electorates which are struggling to get good female representation. The party has 14 women among its 34 MPs.
The ban is one of the proposed new rules for the constitution, which will be considered by the party at its annual conference in November.
Women's Affairs Minister Jo Goodhew told Radio New Zealand's Morning Report programme on Friday people should be selected on merit alone. She said New Zealand has a proud history of women succeeding in politics based on their competency.
Labour women's affairs spokeswoman Sue Moroney told the programme anything that boosts the number of female MPs is a good thing and more balanced gender representation in Parliament will lead to better decision-making.
However, leader David Shearer said he does not support the idea of a quota and the party should set targets to get more women in Parliament.
Party president Moira Coatsworth said the proposal will not cause a rift among the members. She said Labour strives to be progressive in its thinking and the gender equality idea has already been a success with the Labour Party in Britain.
Ms Coatsworth said that, if adopted, it would make Labour more representative of New Zealand's population.
The proposal has prompted vigourous debate on Facebook among Labour activists, with some warning it is another example of political correctness which could play into the National Party's hands. Others say Labour will never get proper gender balance without changing the rules.