The Minister for Women, Paula Bennett, says gender bias does exist and employer's sometimes think they can get away with paying women less.
The 12% gap between what men and women are paid hasn't changed for the past decade and employers are being told they can close the gap if they want to.
A report by AUT for the Ministry for Women surveyed more than 13,500 people and also found the size of the gender pay gap increased for men and women employees on higher incomes.
A pay equity expert says the new research confirms the widespread sexism against women in the workplace and shows 80 % of the gender pay gap is due to conscious and unconscious bias against women.
The minister Paula Bennett says there is no good reason for women to be paid less than men, and that admitting there is a gender bias is a way to overcome the problem.