This is a bit of the Holy Grail for me. Social Media + Legal + HR Policy = Lawsuit
Short version of what will become a long story:
A customer made a complaint about an employee who was asked to prepare a report on what happened. She asked for and was denied access to a union rep. That evening she hopped on her personal computer at home and wrote some not nice things about her supervisor and some coworkers joined in.
The employee was terminated.
The employer, American Medical Response, has an Internet policy and says the employee was in violation of it.
The National Labor Relations Board is saying something about "concerted activity" between employees.
The difference being if she has said her supervisor sucked and was a horrible person she might not be protected but because others joined in talking about workplace conditions she may be.
Click National Labor Relations Board for their statement.