Americans can speak their minds as they wish in many places, but your workplace isn't one of them. First Amendment free-speech rights do not extend to the private workplace. So don't let employees hide behind the cloak of "free speech" in trying to avoid punishment for inappropriate comments.
Recent case: A school principal and a teacher's aide sued their school district after receiving reprimands for spreading gossip about an incident they witnessed involving other teachers. The pair claimed that the disciplinary measures violated their First Amendment right to free speech.
A California appeals court rejected their arguments, saying their comments "were simply a rehash of the salacious details" of what the aide had witnessed, rather than the protected actions of a whistle-blower. (Thompson v. Mt. Diablo Unified School District, No. A097629, Cal. Ct. App., 2003)
Final point: Employees can't claim they are protected "whistle-blowers" unless they're shedding light on a safety concern or illegality. Blowing the whistle on some minor company rule violation doesn't count.