The fact that other employees have participated in pro-employee activism and not been disciplined speaks to that. Some things are fine, some things are not. Abusing security software is not.
Do you activism in your personal time. Don't use important company resources used to protect employees from harm to push your slogans. Regardless if those slogans are legally legitimate statements in a normal context, like handing out a leaflet on the edge of the property.
Correction: an internal message display tool.
> for your own pet activism
> push your slogans
Correction: a warning not to break federal labor law, which Google is actually required to provide.
https://miro.medium.com/max/2000/0*1BTVYLTvuHiJVvp_.jpg
> Do you activism in your personal time.
This is about Google. Apparently their company culture has been the opposite, and they have commonly had lots of political discussions on company time using company resources.
For the millionth time, it was not a general message display tool. It is a security tool to flag domains that run the risk of data leakage and malware. Trying to hijack a security extension to turn it into a general messaging platform is both stupid and bad for security.
Labor law requires that those notices be posted somewhere in a prominent place employees are likely to see. They definitely don't require them to be posted in arbitrary places at any employee's choice.
(Furthermore, the laws about protected concerted activity specifically permit you to do your activism at work, not just on your own time.)
Jeez, politics really does make people go funny in the head. As long as it's "their guy" everything is on the table to sidestep logic.