The company says it has seen a marked increase in reports of employers or others seeking to gain access to people's Facebook profiles or private information.
"This practice undermines the privacy expectations and the security of both the user and the user's friends," Erin Egan, Facebook's chief privacy officer, said Friday in a Facebook post. "It also potentially exposes the employer who seeks this access to unanticipated legal liability."
The company said it is most concerned with instances in which employers ask prospective or actual employees to reveal their passwords.
"If you are a Facebook user, you should never have to share your password, let anyone access your account, or do anything that might jeopardize the security of your account or violate the privacy of your friends."
Facebook said it has made it a violation of the company's Statement of Rights and Responsibilities to share or solicit a Facebook password.
The company warned employers could open themselves up to claims of discrimination if they see protected information, such as a person's age, and then fail to hire them.
Facebook said it will use legal means, if necessary, to protect the privacy of Facebook users.
"We'll take action to protect the privacy and security of our users, whether by engaging policymakers or, where appropriate, by initiating legal action, including by shutting down applications that abuse their privileges."