> How do you arrange something like that behind your boss's back if you can only communicate with your colleagues via corporate-approved communication channels?

I'm a Betriebsrat, a Germany-specific "workers council", member at my employer. By law, the company is mandated to provide us with the resources we need (e.g. access to company wide email distribution lists, a private MS Teams channel, private folders on the file servers, a locked office for personal meetings of the council and with staff members) and is prohibited from interfering with all our duties. Any form of censorship or surveillance would be a big no-no which could even land our execs behind bars.