Since the 1940's, the labor force participation rate of women has increased on a consistent basis, and today as many or more women as men engage in paid employment. It is also true that women have consistently increased their average years of education over this period of time. (Although not always in the highest paying occupations.) The "wage gap" is defined as the difference between the average pay per hour worked for women versus the average pay per hour worked for men. This is often expressed as something like: "Women earn on average only $.78 for every $1.00 that men earn."
The difficulty with this comparison is that it includes many factors that are legitimate (i.e. not sex discrimination) reasons for pay differences, such as less work experience; self selection into lower paid occupations (e.g. public school teacher rather than perhaps engineering); choosing employers who offer higher employee benefits (not included in calculation the pay gap) and correspondingly lower cash compensation, fewer hours per worked per week, etc. Self-selection, or the choices women make, are usually seen as legitimate differences in average compensation.
You'll find some general discussion of the issues here:
http://en.wikipedia.org/wiki/Male%E2%80%93female_income_disparity_in_the_United_States#Explaining_the_gender_pay_gap
You'll find the actual "Gender Wage Gap" study here:
https://www.dropbox.com/sh/djnqk52bre5lpcg/ukXvHeGBQv
In 2009, the U.S. Department of Labor commissioned a study to review all existing empirical studies of the male - female wage difference. This study was quite well done, and concluded that most (almost all) of the difference between men's pay average, and women's pay average was due to choices that women made, such as occupation, time out of labor force, working fewer hours, etc. I am attaching a copy of that report to this message.
THE DEBATE should focus on:
1) Does a pay gap between men and women exist?
2) What is the size or amount of that pay gap?
3) Why such a gap in average pay does or does not exist.
4) If you are arguing in favor of additional legislation, sketch what this law would include and how it would work.