Listed companies will be required to disclose how many women they have on their boards and in senior management, the NZX announced last night.
The new diversity rule, still subject to the approval of the Financial Markets Authority, will be applied to the annual reports of companies with a balance date on or after December 31.
In addition to publishing a gender breakdown of directors and senior management, firms with a formal diversity policy will be required to evaluate their performance with respect to that policy, NZX said.
The new rule, however, does not require companies to implement a formal diversity policy. NZX chief executive Tim Bennett said quantifying gender composition at governance and senior management levels was "an issue of importance to our markets".
"However, it's important that we give our listed companies the flexibility to make their own decisions about whether a formal diversity policy is a priority for them at this stage."
The NZX would like to see more listed companies taking the opportunity to report on diversity, he said.
NZX said there was credible evidence that suggested diversity, particularly around gender, at both board and senior management levels contributed to improved financial performance.
"NZX is also conscious of the need to balance provision of information to investors with the ongoing compliance costs to issuers," the stock exchange operator said.
"Therefore, in response to the feedback NZX received during the consultation process, a number of changes to the proposed rule have been made which give companies flexibility around their decisions to develop a formal diversity policy while encouraging them to do so and to set measurable objectives."
The NZX's new rule brings New Zealand into closer alignment with Australia, where similar requirements introduced by the Australian Stock Exchange resulted in a big jump in the level of female representation on listed company boards.
As of last August, 12.7 per cent of Australia's top 200 listed firms had women directors, compared with just 9.3 per cent for the top 100 listed companies in this country.
Fisher & Paykel Healthcare, Mainfreight, New Zealand Oil & Gas, Infratil, Cavalier Corp and GPG are just a few of the NZX-listed firms that currently have no female directors.
And the Business Herald's latest executive pay survey, which covers most of the chief executives of New Zealand's biggest listed firms, did not feature any women for the first time in its eight-year history.
Earlier this year high-profile businesswoman Diane Foreman told the Business Herald she thought publicly listed companies should at least be required to "cast their net far and wide" when searching for board appointees.
"If you start with a male board, the people they're going to ask to be directors are usually going to be somebody they know from previous incarnations or from the golf club," said the Emerald Group founder and chief executive.
The old boys' network theory is backed up by research released earlier this year by Harvard Business School professor Boris Groysberg.
His survey, which canvassed a sample of male and female ASX 100 and NZX 50 directors during the final quarter of last year, found the overwhelming majority of respondents cited their networks as the source of their board seats.
The survey also found male and female directors had "polar opposite" views on the reason for lack of gender equality in the boardroom.
Sixty per cent of male board members attributed the disparity to an insufficient number of female senior executives, but 70 per cent of women directors thought the problem stemmed from a lack of access to male-oriented networks.
NEW NZX RULE
The new diversity rule will require listed firms to:
* Provide a breakdown of the gender composition of their directors and senior management.
* If they have a formal diversity policy to give an evaluation of their performance.