In an internal memo obtained by website Business Insider, the social network's chief technology officer Mike Schroepfer said on Monday that the Facebook has developed "a set of ground-rules for open and respectful communication at work, and a central moderation model".
Workers will be prohibited from attempting to change their colleagues' religion under the new rules.
Speech deemed as harassment and any bullying will also be banned.
Most of the rules apply to Workplace - Facebook's modified version of the Facebook app for internal communication.
Schroepfer added: "We're keeping it simple with three main guidelines: Don't insult, bully, or antagonize others.
"Don't try to change someone's politics or religion. Don't break our rules about harassing speech and expression."
The rules will also apply to "all work communications" including, "email, chat, tasks, posters, whiteboards, chalkboards, and face-to-face".
The Silicon Valley tech giant has defended the guidelines following the Business Insider's publication of the internal memo.
Facebook spokesperson Anthony Harrison said in a statement: "Openness is one of the best things about working at Facebook.
"And respect is core to who we are as a company. This policy is designed to encourage everyone who works here to keep sharing, debating, and questioning - with some simple guidelines to assure communication is respectful."
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