In their efforts to screen job applicants, some employers are going beyond the usual questions about experience and references and asking for something else: Facebook usernames and passwords.

The practice seems to be more common among public agencies, especially those seeking to fill law enforcement positions such as police officers or 911 dispatchers. But it's happening in both the public and private sectors, and some job candidates cannot afford to say no.

Orin Kerr is a George Washington University law professor and former federal prosecutor. He says the practice is like "requiring someone's house keys."

Companies that don't ask for passwords have taken other steps -- such as asking applicants to friend human resource managers or to log in to a company computer during an interview.