I wonder if this has been challenged at the Supreme Court level (1st amendment, freedom of speech and all that).

I would be surprised if disparaging a corporation is protected the same as disparaging an individual... but one never knows in this crazy world.

I know an employer can establish policy, but in doing so, I don't think they can violate the Constitution.

(Of course by disparaging, I mean writing verifiable facts that might not be pleasant to read, but are true.)