How certain are you this happening? Have you talked to the cofounders? I'm not suggesting its not happening, and its certainly a lawsuit if it is the case but be damn sure that they are doing it before you take any legal action/go open with it. It would destroy you along with them if you take it to the public and you are wrong. If you can without a reasonable doubt say that they are, and have evidence that isn't based on negotiations or bonuses, then by all means sue them in court: you are owed money. This is a really hard case to prove though because the burden of proof is on your and thus you must be able to prove via emails from the founders/HR or recorded chats (concrete admissible evidence) of them saying to discriminate against people or its just slander. If you slander or libel them without proof, you will get sued and you will lose. It will also damage your reputation and future career prospects. Just because your salaries are lower doesn't mean there is discrimination; the other people could have negotiated better or negotiated at all. There can be other more innocent things as well such as buddies of the founders getting paid more not because they are men but because they are friends. There are a lot of scenarios at play here, and if they are discriminatory I hope you the best to win the case. Nobody deserves to be discriminated against.