Could you share any citations?
Thus far, when trying to research this issue, keep running into the well-debunked The 76 cents (or 72 cents or X cents) on the dollar myth that still enjoys popularity amongst feminists.
Unfortunately, that statistic simply compares the earnings of full-time workers with the same job category. It ignores the hours of work per week, experience, danger, and a host of other factors. It quite literally compares the salary of people with years of experience who are working 60 hours a week directly with new hires of the same job title who are working 40 hours a week. It lumps them all together.
Study after study I've seen which have actually controlled for factors such as experience, hours worked, travel required, etc have found very little pay disparity. This NCPA article is a brief explanation of The Wage Gap Myth:
http://www.ncpa.org/pub/ba392 http://www.iwf.org/campus/show/18948.html
The Cato institute and others have done more in depth analysis.