UPDATED 4.52pm The Government has admitted work is needed to close the gender pay gap, but won't bring in hard and fast targets.

Figures released by the State Services Commission show some Government departments have as much as a 39 per cent pay gap between men and women.

The biggest gaps are at the Ministry of Defence and Crown Law.

Minister for Women Louise Upston said they're focused on encouraging businesses to support women through measures like more flexible work.

"The fact that in the private sector we have got a pay gap of 11.8 per cent and in the public sector of 14, clearly we've got work to do."

Upston said it's about encouraging employers to be more supportive. 

"I don't believe we need to set a target, we need to continue to monitor and report on it, and as I said last year when it did bounce up a bit it was intensely frustrating, but there's a lot of work going on."

But Green Party co-leader Metiria Turei said nothing will change unless the Government sets targets, and holds departments to them.

"Government departments can fix it, in the way that they structure their pay scales, and they should fix it.

"It's not complicated, they just need to make the effort."

Turei said if there is no emphasis from the Government to ensure women are paid properly, then there's no motivation for Government departments to do anything.

Labour's workplace relations spokesperson Sue Moroney said the figures disprove those who think the gender pay gap isn't a real problem.

"If you work in Crown Law and you're giving legal advice, you should have the same opportunity to be promoted, and you should be getting paid for the qualification and for the advice that you give."

The Public Service Association said it's disappointed, but not surprised at the figures.

PSA National Secretary Erin Placzuk said most of the union's members are women, and the public sector can be leaders in creating equal pay.

"And I think it's time for the Government to step up, take some leadership and show our members that they think the Government values them and thinks they're worth 100 percent."