The pay difference between women and men is worst in Western Australia, Australian Bureau of Statistics figures show.
There's a $483.80 per week gap between the full time, seasonally adjusted earnings of men and women in resources-rich WA, where both genders bring home the nation's biggest pay packets.
The next worst state for the gender pay gap is NSW, with a $316.60 per week difference.
Pays were fairest in South Australia, which had a gap of only $151.20.
And while Tasmanian women pocketed the nation's most modest weekly sum at $1187.30, the gender difference was only $159.60.
UnionsWA secretary Meredith Hammat said it was inequitable and wrong that WA women earned 25 per cent less than men.
"When women take on caring roles, the pay gap can be entrenched for the rest of their lives including into retirement through lower superannuation," Ms Hammat said.
"This means women are more likely to be financially insecure.
"Women are more likely than men to have to meet family costs of living that are already high in WA."
She called on governments and employers do more to support women in the workforce and assist with the costs of caring.
"Stronger measures are needed to address pregnancy discrimination in the workplace, whether it's losing permanency after returning from maternity leave or employers refusing requests to work flexible hours."
