People supporting a software engineering union are looking for equality in the group, even though every member of the group is already objectively doing pretty

People supporting a software engineering union are looking for equality in the group, even though every member of the group is already objectively doing pretty well. I personally worked with many women who were just as smart and productive as me, but got paid less. Why is that? There are many reasons; self-selection for promotion was noted as one reason at the time. Managers need to encourage employees to go through the promotion process, but managers don't do this consistently. The data shows that the result of this is that there is a gender gap in pay, and that doesn't feel very good. Some system other than individual managers encouraging people to go up for promotion is needed; a union looking out for that is one solution. I don't know how it would work, I'm not really up to speed on how to organize a union or anything, but issues like that is where the core of the support comes from. (The article also mentions binding arbitration clauses being another sticky bit.)