How can this be legal? They can ask, but do you have to comply? What if you tell them you don't have an account, can they fire you? Under what system of government are people told to disclose a personal password to a web site to their employers? What if I give them the password, then change it?
What if items are found on these sites that are considered firable? How can the employer justify the method of attaining the information? Is this not against the constitution of the US? Where are my fifth amendment rights?