An Auckland University of Technology report said yesterday those traditional excuses actually made up just 20% of the reasons Kiwi women earned, on average, 12% less than men.
Women's Minister Paula Bennett said the news that 80% of the gender gap was caused by an unconscious bias was"really disappointing''.
In her first major speech in the portfolio, Ms Bennett called on employers to hold a gender pay audit.
"It's simply unacceptable that women who are as productive and contribute so significantly to business and the economy are paid less than men,'' Ms Bennett told the Human Resources Institute of New Zealand conference in Wellington yesterday.
Researchers said the fact women were now more highly qualified than men should be reducing the gender pay gap.
In response to the research, Ms Bennett called on businesses to look at whether women were being promoted into positions they deserved and offered clear career progression criteria.
The Human Rights Commission said the research revealed a need for urgent and deliberate action to combat workplace bias, while Equal Employment Opportunities Commissioner Jackie Blue said the results were worse than expected.
"Negative biases and stereotypes are continuing to impact the recruitment, pay and promotion of women in the New Zealand workforce and that's unacceptable,'' she said.
"We need urgent, deliberate and affirmative action at all levels, to combat the issues they face.''
She backed Ms Bennett's calls for employers to regularly audit wages and for them to publish pay gap data.
Labour leader Andrew Little acknowledged yesterday that "decades and decades of discrimination, prejudice [and] undervaluing women'' were to blame for the pay divide.
Mr Little's message to employers was it was "time to get into the 21st century''.
Public Services Association national secretary Erin Polaczuk welcomed the research, "as depressing as its findings are''.
She said the onus was on the Government to fund the Ministry of Business, Innovation and Employment to implement and enforce labour standards.
"This Government's moving in the right direction, but a lot more needs to be done before New Zealand employers are truly paying women what they're worth - 100%,'' she said.
