My experience with unions from from (a) conventions centers and (b) aerospace. In both, they are a net negative from my POV.
At convention centers they inflate prices by passing rules that no one but a union worker can carry anything into the convention center. The monitor broke and your booth and you run to best buy to get a replacement. Sorry, find a unionized person to carry it in for you or GTFO. Oh, you want to plug in it in? Sorry, call a unionized electrician or be sued.
An aerospace it meant everyone's role was super strict and trying to do anything outside your role was against the rule. In software that would mean things like front end programmer not allowed to touch backend code. UI programmer not allowed to touch business logic code. Etc.... Maybe someone will argue that's a good thing but AFAICT it just slowed work to a crawl and made people uncooperative