Asymmetrical Information has a lengthy post on a small but growing trend of bloggers having to shut down due to pressure from employers. Eugene Volokh also weighs in.
Unless the blogger is acting in a way obviously against the interests of his employer, I can’t see why it would ever become an issue. As long as it doesn’t take up too much time, even a little on-the-job blogging strikes me as beneficial for employers, as it indicates that the employee is keeping up with the news and honing his analytical and communication skills. That said, I tire of endless whining about the 1st Amendment. Private suppression of speech is NOT a violation of the a person’s civil liberties. The Constitution is designed to protect us against governmental tyranny, not short-sighted bosses.
