Interestingly, I just read a CNET article on this very subject. Facebook has indicated that it is actually against their use policy to provide that information. Here is a direct quote from the article:
Companies making such requests may not have the right policies or training in place to deal with private information, according to Facebook. Further, companies might be held liable if the information they find proves problematic, such as a post that "suggests the commission of a crime."
Credit CNET March 23 "Facebook: Don't reveal your password to snooping employers" by Lance Whitney