From my read of the situation (based on past union experience), this is not a normal union. They do not seek exclusive bargaining power for a contract.
It seems more like an association of employees who seek to influence leadership on specific topics. There influence comes not from the threat of a strike, but rather just numbers (eg we have X% of workers, all willing to put up 1% of pay, you should really listen to us).
In that case, for an average employee making $100k-$200k a year in base salary at Google, I can't imagine paying $1-2k a year for the privilege of raising concerns without any real teeth. They can already do this anyway in retros or all-hands meetings, signing on to open letters to the executive team, etc.
Not saying that the organizers here have malicious intentions, but if you did have malicious intentions then something like this could actually be a pretty good scam... Re-purposing the word "union" for something that is not really serving that role, and collecting money from people who will ideologically sign onto it without thinking because they automatically think "unions == good". Basically making money off of the current shift to the left in US politics.
It seems more like an association of employees who seek to influence leadership on specific topics. There influence comes not from the threat of a strike, but rather just numbers (eg we have X% of workers, all willing to put up 1% of pay, you should really listen to us).