As a matter of fact, at one point, for a number of years, my sister did exactly the same job as male co-workers, put in as many hours or more on the same projects, taking the lead on some---and got paid less. Ostensibly because her job title was slightly different but it turned out that indeed there were one or two men with the same job title who were paid more. After spending some time trying to convince tptb that she should get the same pay, she took our father's advice and simply insisted that her job title and subsequently the same pay.
That's been some years ago but it was a very common practice: to give men and women different job titles and different pay grades but the same job duties. One job title was of course in line for more promotions. Women were assumed to be just killing time until marriage and kids, never mind that a woman may have no such plans. A man on the marriage/kid tract was seen as more responsible.
It's different now but at my workplace, a woman who has a baby is still seen as less dedicated and more likely to leave. All data to the contrary.