But up to 84 per cent of the reasons for the pay gap were attributed to "unexplained factors".
"That means it is bias against women, conscious and unconscious.
"It is because there is still a belief that women will accept less pay than men - they don't know their worth and aren't as good at negotiating.
I'm here to tell you it's no longer acceptable to keep ignoring this issue.
We need to consciously work together to put this right.
Bennett challenged human resource managers to examine their own practices.
"When you go to hire someone, do you put forward a list to your employer that has gender balance?
"Do you question why women aren't putting themselves forward for roles that they're clearly capable of doing?
"Do you encourage women to have a shot at it?
"And do you encourage your employer by putting women forward to them?
"Do you actively seek women out when they're not coming forward themselves?"
She said the first step was to recognise there was a problem.
"A gender pay audit might be a good way to find out if there is a problem.
"Look at whether women are being promoted into positions they deserve. Are you shoulder-tapping people when they're worthy of promotion?"
Often women were recruited but not retained or moved to senior management.
Bennett held up Prime Minister Bill English as someone who strived to do better for women in board appointments, when he was Finance Minister.
He would often receive lists from Treasury that were mostly if not entirely men.
He would send the list back to Treasury and wouldn't consider making appointments until he had women to choose from as well.
Forty-eight per cent of his board appointments as Finance Minister were women.
Bennett said that when she worked in recruitment, she used to challenge women to put themselves forward.
"I've been the woman fighting for a promotion - you may have heard I did it quite recently - going for the deputy PM role.
"In my teens and through my 20s I was plagued by self-doubt and low confidence. Not anymore. I knew I was the right person for the job. I also knew some would question me about being the Minister for Women.
"I would be 'too something' for just about everyone. Too stroppy, too weak, too old, too young, too feminist, not feminist enough. That one is interesting. Feminism means different things to different people these days. I am very comfortable being a feminist. I don't judge others who sit in different places on the spectrum - they of course get to judge me, but that is called politics," she said.
She was now a mentor to some in Parliament, and to some who want to get into Parliament.
"It might surprise you to know this, but even as Deputy Prime Minister I still sought out a mentor, outside of politics, to provide me with support and advice.
"Asking for guidance and leaning on others occasionally is not a sign of weakness but in my view a sign of strength."
She wanted to challenge attitudes to reduce the 12 per cent pay gap over the next decade.
Bennett said employers had to remember three things.
"It's not about what you can get away with; it's not about what she is willing to accept; it's simply about you paying her what she is worth."
The research was led by Professor Gail Pachecho if Auckland University of Technology on behalf of the Ministry for Women's Affairs.
