Have the WMF done something bad that needs counterbalancing or are they just forming a union out of some sort of principle?
They recently laid off an internal team that was popular among workers and also fired one of the oldest employees for dubious reasons. Notably all of the people laid off or fired were union advocates, so this can be seen as a supercharged reaction to an effort to union bust (whether it was or not, it was certainly perceived that way).
unions are institutions for bargaining power, even under decent employers