Growing use of social media outlets has prompted dispute over whether or not the protections of the First Amendment extend to websites such as Facebook and Twitter for employees. Labor lawyers say that the answer lies in whether the speech is considered to be concerted. Usually an activity is concerted if more than one employee is involved, say if one employee posts something about his employer and another employee comments on it. The First Amendment net for public employees is less wide, usually only protected if the speech alludes to matters of public concern.
See "Social media free speech rights complicated for workers", Kristi Marohn, USA Today, July 7, 2013