Fair warning, this topic has been beaten to death and is now radioactive and everyone has settled in their tranches. But just Google around and you'll find tons of resources, though the wikipedia page[1] has a good overview of some of the subtleties, and some good examples (the recent Uber study is referenced on the page). And the fact that there are deep, nuanced, subtleties that require context to properly digest shows you that activists are really dishonest whenever they make shallow claims of wage discrimination.
For the sake this next example, grant me that difference in wages is due to life choices, even in that case, you can reach a state where things are, on the surface, unfair, like for example the fact that the pension will be greater for men than for women (or vice versa if we're talking about a female dominated field). You can take a shallow view and look at the raw numbers and assert bigotry. But that misses something, because it isn't quite the same as a government having a policy where, even when all things are equal, women get a low pension rate.
Almost every single explanation or example has this kind of nuance. It is almost never the case that someone just decided that Jane should make less than Bob because he's a man and she's a woman (though I'm sure in a country of 350 million, you can find plenty examples of that too). Furthermore, no company, and no government department has policies on the books that mandate one gender should be paid more than the other, and in fact they all have policies to disallow that - which really cuts against the claim of systematization (how can it be systematic if everyone is actively against it).
[1] https://en.wikipedia.org/wiki/Gender_pay_gap