The Alphabet Workers Union is fairly toothless. It has no legal power, is not officially recognized by Google, and has no contract or formal bargaining power.
Legally-recognized unions with employer contracts don't spring full formed from the head of Samuel Gompers, they are the result of organizing efforts that spend a time as unrecognized unions.
> We will ensure Alphabet acts ethically and in the best interests of society and the environment. We are responsible for the technology that we bring into the world, and recognize that its implications reach far beyond Alphabet. We will work with those affected by our technology to ensure that it serves the public good.
To be honest, this strikes me as an incredibly pretentious opinion from people who have drank too much of the Google Kool-Aid.
Then their initiatives are focused on contractors, which don't really incentize employees to join, and larger public social justice where the union might lack sufficient teeth to effect change.
There isn't really enough self-interest to join, so your average Googler is probably better off taking the company match on a philanthropic contribution.