It's not the union choosing to promote, it's the employer for IBEW.
Also disallows noncompete clauses. So if your current employer says no, you can go to another. Which is how I've seen quite a few promotions. The latter of switching employers is far easier, since life changing benefits (medical/retirement) aren't tied to employers. (Considering SV workers get their "share" by switching employers every few years, that would be a nightmare scenario for big tech as well. Since it further reduces employee stickiness, if SV unions decided to offer benefits).
Also disallows noncompete clauses. So if your current employer says no, you can go to another. Which is how I've seen quite a few promotions. The latter of switching employers is far easier, since life changing benefits (medical/retirement) aren't tied to employers. (Considering SV workers get their "share" by switching employers every few years, that would be a nightmare scenario for big tech as well. Since it further reduces employee stickiness, if SV unions decided to offer benefits).