Since everybody knows that, only the most sketchy employers consider something along these lines. Again one ofnthe reasons I am really happy with my job and the country I have it in.
The heavy monitoring of communications, access etc is mandated by regulators primarily for the protection of customers. There's zero chance a union, or any other body below government, will get them to change that. I doubt they'd even try and nor should they.
I also don't believe for a second that JPM are doing what the original post is saying they're doing in regard to private devices. It would be astonishingly expensive and illegal in some jurisdictions. And thousands of people would need to know, in detail, for it to be useful so wouldn't just have come out in a subreddit. It would be widely known in the industry (and it isn't).
Any union of citizens will have power.