AustralianSuper, which manages almost $170 billion in retirement savings, plans to write to ASX-listed companies warning them it will vote against the most senior director up for reappointment if they have fewer than two women on their board.

The move will target 52 of Australia's top companies, over a quarter of the ASX200. AustralianSuper instituted a policy in 2016 of voting against the next director up for re-election of ASX 200 companies with no female directors.

At the time, there were 17 companies without a single woman on the board, but now only five companies have no women at board level. Most ASX companies will hold their annual shareholder meetings in coming weeks.

Andrew Gray, director of environmental, social, governance and stewardship at AustralianSuper, said the fund wanted companies to demonstrate a commitment to increasing the number of female directors to two.

"We just don't think it's acceptable [...] for an ASX200 company," he said of the lack of women on boards. "So I don't think there's actually an excuse for it."

Mr Gray said AustralianSuper's push for more women on boards was all about investment outcomes.

"Companies with better gender diversity on their boards perform better," he said. "That makes them better investments and therefore generate better investment returns for our members. So to us, the case for gender diversity on boards is clear."

Mr Gray said AustralianSuper would not vote against a woman director who was up for re-election as that "would be counterproductive".

Mr Gray said AustralianSuper, which holds about $40 billion worth of Australian equities, expected a "gradual response" over the next three years to its push to make ASX200 companies have two women on each board.

"It really is company specific," he said. "Looking at the numbers, I mean, 50 companies, that's a large number. The reality is, that director pool, the director pipeline, is a challenge in getting that solved short term. It's not a small task."

The move is in line with the voting guidelines issued by the Australian Council of Super Investors (ACSI) in March to vote against the most senior director seeking reelection at companies with one or zero women directors.

ACSI chief executive Louise Davidson said one-woman boards were a focus for her organisation's members, with the aim of having 30 per cent of the board positions in ASX-listed companies held by women.

"Having one woman on the board does not represent job done," she said. "As we have seen before, these boards can easily revert to zero women directors."

Australian Institute of Company Directors' manager of advocacy Louise Petschler said voting against directors was a "powerful intervention" in the market.

"Those investors are free to make their own decisions on the companies they invest in," she said. "We absolutely respect that is their decision. For some investors it won't be as important as it is for others."

The five ASX200 companies without a single woman on their board are Emeco Holdings, HUB24, NRW Holdings, Pro Medicus and TPG Telecom.

The chief executive of Emeco, Ian Testrow, said the company had engaged a recruitment firm to find a female director.

"It is not by choice that we haven't got a female, we had one, she got restructured out, we are working hard to replace her," he said.

A spokesperson for Hub24 said the company was committed to diversity in its board and had commenced the recruitment process for a new non-executive director. The other three companies did not respond by the publishing deadline for this article.