'If you are a Facebook user, you should never have to share your password,' Facebook advises.'If you are a Facebook user, you should never have to share your password,' Facebook advises. (Associated Press)

Facebook is warning employers not to demand the passwords of job applicants, saying that it's an invasion of privacy that opens companies to legal liabilities.

The social networking company is also threatening legal action.

An Associated Press story this week documented cases of job applicants who are being asked, at the interview table, to reveal their Facebook passwords so their prospective employers can check their backgrounds.

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In a post on Friday, Facebook's chief privacy officer cautions that if an employer discovers that a job applicant is a member of a protected group, the employer may open itself up to claims of discrimination if it doesn't hire that person.

"If you are a Facebook user, you should never have to share your password," Erin Egan wrote.