In a training class I took, some time ago, the instructor stated that supervisors always represent the city.  The trainer basically stated that comments made by a supervisor are always something an employee can use for a case/claim because you cannot take off your supervisor hat.  I took that training a long time ago, so I cannot remember if it was based in "fact" or a best-practice.

Is there any legal precedence for this?

What is happening is I have "gossip" going around and I have exempt employees sharing information with non-exempt/hourly employees that should not be shared (bargaining, management conversations, etc.).  I've explained what they say impacts the city or the ability of managers to do their job, but they are not changing their behavior because they are talking with their friends.  I cannot "cite" anything that puts it in black and white for them, and they are not doing anything outside of our employee manual.  Thoughts?