I think its entirely reasonable for an employer to monitor employee communications on company media channels. I've dealt with a few toxic employees in the past where their incessant complaining and passive sabotage of work is incredibly harmful to morale and work of others.
I don't really see how using AI is controversial other than it's being done more efficiently, flagging just blatant violations. Seems preferable and more respectful of privacy that having an employee read all communications manually and applying judgement.