This article makes the point the governing law on what an employee handbook can restrict in terms of employee rights to discuss wages and working conditions is governed by a 1998 opinion not the settlement in the American Medical Response case where the employee complained about her manager.
Takeaway?
Employers when spelling out what employees can’t say or do in terms of expressing themselves about their employer, need to be specific and need not be in the realm of wages or working conditions.
For example, a clause stating that the employee is not to make derogatory remarks about the employers logo or brand, that would probably pass muster because that clearly doesn’t impact wages or working conditions. An employer would be wise to list out a series of situations that are restricted and then state the prohibitions aren’t “limited to” these but it would give the worker a clear idea of what they aren’t allowed to say.