Equal Pay Today! Campaign Member Organization -- ACLU Women's Rights Project -- pens a blog on the stagnant gender wage gap.

ACLU Blog: "Some Things Change With Time … While the Gender Wage Gap Remains Relatively the Same," By Lenora Lapidus, Director, ACLU Women's Rights Project

There are many reasons for the gender wage gap. These include women being paid less than men for the same or comparable jobs, job segregation in which women are concentrated in the lowest-paying fields, and pay reductions due to pregnancy and caregiving responsibilities. A major impediment to women gaining equal pay is companies’ lack of transparency in their salary scales and retaliation against employees who discuss their salary.

Obama has done what he can with executive orders. In July 2014, he made it illegal for federal contractors to retaliate against workers for discussing their pay, and he required those employers to regularly report to the Department of Labor its compensation figures, broken down by gender and race.

And some members of Congress have continued to fight on, introducing the Paycheck Fairness Act every year since 2007. This federal bill would strengthen current law to make it possible for workers to know where they stand in comparison to their colleagues by prohibiting retaliation against workers who discuss their salaries, while making it easier to prove discrimination — even if they have different job titles. For example, a “housekeeper” wouldn’t make less than a “janitor” for doing comparable work.
And several states are stepping into the breach as well, enacting stronger wage protections for women than those available under federal law. Indeed, legislators in approximately 24 states this week introduced bills to close the gender wage gap. Advocates in several of those states are now working together as part of the Equal Pay Today Campaign, to coordinate state-by-state advocacy and build momentum towards gaining equal pay throughout the country.
— https://www.aclu.org/blog/speak-freely/some-things-change-time-while-gender-wage-gap-remains-relatively-same