I think you might be arguing against a straw man here, or recalling an argument with some rather misinformed opponent.Please do show me a study that shows that men and women get paid differently _ for the same work_.
Gender pay gap takes into account the median wage across the economy. It reflects a range of biases in employment, including gender preference in filling high-paying (leadership) positions or being employed full time, or being promoted. But, it also includes preference for the female to take a break from a career to raise children, or educational choices - which reflect wider societal biases than just those occurring at the workplace, as well as actual legitimate lifestyle choices.
That's where the so-and-so many cents per dollar statistics come from. The data are available from government websites (or e.g. OECD's).
Pay gap for equal work can figure in there as a factor, but in your country it is illegal (as far as I understand the situation, it's covered by the 50-year old Equal Pay Act?). For a proof that this exists you shouldn't look at studies, but at occurrence of lawsuits that end up awarding damages (e.g.http://www.eeoc.gov/eeoc/statistics/enforcement/epa.cfm).