Does an email server processing n emails per second require more power to process n+1 emails per second? My suspicion is that unless that +1 hits some capacity limit, the number of emails we're talking about required to organize union activities would be undetectable.

That said, even if it is detectible, I think that employees should be allowed to drain some small amount of a company's resources to organize. I am allowed to use company resources for emails like "who wants to go for beers after work?" why should I not be allowed to send "who wants to go organize collective action after work?"