Statistics NZ's quarterly employment survey shows women's average hourly pay rates rose from 72 per cent of the male average in 1974 to a peak of 88 per cent in 2009, but have fallen back slightly since then to 86.5 per cent of the male average this June, the widest gap for nine years.
The gap is partly because many female workers are concentrated in lower-paid jobs such as caregiving - a factor behind legal challenges first by caregiver Kristine Bartlett and now by the College of Midwives.
But the available data also shows men earn more than women on average even within individual workplaces. For example, men earned more than women on average in 30 out of 32 state departments in 2012.
Auckland YWCA chief executive Monica Briggs said most organisations that entered the agency's first Equal Pay Awards last year still paid men more than women on average, but one paid women more on average and "some of the others have got it down to almost zero".
The survey found only 11 per cent of women and 10 per cent of men felt they had experienced pay inequality because of gender in the past year.
But 41 per cent of women and 26 per cent of men agreed "men are given more opportunities in your workplace to get paid more".
The statistics show the gender pay gap closed most in the years immediately after the Equal Pay Act of 1972, and in periods of economic growth in the late 1980s and from 1997 to 2009. The pay gap stalled during tougher times from 1977-84 and 1990-96, as well as since 2009.
AUT University economist Dr Gail Pacheco said the long-term narrowing trend reflected women surpassing men in educational achievement, but the remaining gap could be due to discrimination.
"It could also reflect that while many of what I would term soft barriers to moving towards equal pay have been removed, there may still be hard barriers such as entrenched attitudes, unconscious bias, etc," Dr Pacheco said.
"Another driver is likely also the glass ceiling effect, ie a gender pay gap still remaining at the top that cannot be explained by individual or job specific characteristics."
Entries in the YWCA Equal Pay Awards close on September 11 at www.ywcaequalpay.org.nz