A series of recent rulings and advisories protect the right of employees to discuss their working conditions on social networks. The National Labor Relations Board, which has reinstated some workers fired for posting on social media, says that they are applying the old rules to new media. The posts are protected if they involve for than one employee and are about working conditions, rather than offensive posts. The Board is also urging companies to rewrite their social media policies in accordance with their rulings.
See "Even if It Enrages Your Boss, Social Net Speech Is Protected", Steven Greenhouse, The New York Times, January 21, 2013