The gender wage gap disappears after controlling for voluntary choices made by women and men regarding occupation, emphasis on family time and duties and/or personal preferences. These decisions often have sociological roots, but they are private decisions in the first instance and not amenable to engineering via regulatory action. For example, controlling for just one factor, marital status, accounts for 75% of the gender difference in average wages. In the post linked above, Mark Perry at Carpe Diem thoroughly debunks the wage gap myth.
It is already illegal to pay equally-situated men and women different salaries. Yet it is just too difficult for some politicians to resist using the difference in average wages as an excuse for regulating private employment decisions and wages. The pernicious effects of this kind of legislation are discussed in ‘Paycheck Fairness’ Will Lead to Fewer Paychecks, Less Fairness. It’s particularly interesting that the “Paycheck Fairness Act” would expose private employers to class action lawsuits over wage differences. Needless to say, trial lawyers are enthused.