9to5's main mission has since expanded to focus on women in low-wage jobs in general. The organization pushes for fair pay measures, paid sick days and maternity leave.

Across all industries and occupations, full-time female workers earned 78 cents to every dollar a man earned in 2010.

In the category of administrative assistants, women outnumber men more than 20 to 1, but still earn less than their male counterparts -- about 87 cents to the dollar.

Full-time female secretaries and administrative assistants earned an average salary of $34,304 in 2010.

For men, it was $39,641.

"The good news is over the past 40 years, there are very few jobs in which women have not broken through," Cameron said. "The glass ceiling is cracking in all different directions, but the bad news is, there is still a sticky floor. Most women still work in traditionally female jobs, like administrative support."