Apostasy is the great spiritual crime of Islám. It was once considered a capital crime, and still is in some circles. The Bahá'í Faith uses its own definition for the term apostasy. The Bahá'í usage of the word implies that apostasy is equivalent to covenant breaking. It is not a capital crime, but is considered a highly contageous spiritual disease, and is therefore subject to severe shunning.
The doctrine of covenant breaking and the accompanying practice of shunning is traceable to Bahá'u'lláh and `Abdu'l-Bahá, but it was formalized by Shoghi Effendi:
Apostates, rebels, betrayers, heretics, had exerted their utmost endeavors, privily or openly, to sap the loyalty of the followers of that Faith, to split their ranks or assault their institutions.
God Passes By, page 408.
When a person declares his acceptance of Baha'u'llah as a Manifestation of God he becomes a party to the Covenant and accepts the totality of His Revelation. If he then turns around and attacks Baha'u'llah or the Central Institution of the Faith he violates the Covenant. If this happens every effort is made to help that person to see the illogicality and error of his actions, but if he persists he must, in accordance with the instructions of Baha'u'llah Himself, be shunned as a Covenant-breaker.
From a letter dated March 30, 1957 on behalf of Shoghi Effendi, "Messages to Canada," p. 64
Bahá'u'lláh and the Master in many places and very emphatically have told us to shun entirely all Covenant-breakers as they are afflicted with what we might try and define as a contagious spiritual disease ...
Shunning is typically done on an individual level, but Bahá'í authorities have also been seen exhibiting this practice. In a recent dispute between the United States National Spiritual Assembly (NSA) and the Second International Bahá'í Council, the WIPO panel that oversaw the dispute voiced some disapproval over the unwillingness of the conplainant (the NSA) to communicate with the other party:
Complainant did not send a copy of its request directly to Respondent, apparently believing Respondent had a “religious objection” to communicating with it. While the Panel appreciates Complainant’s sensitivity, it did not interpret the statement that Respondent had, consistent with Respondent’s religious beliefs, ignored Complainant’s cease and desist letter, to be an objection to receiving communications. Moreover, the Panel reminds Complainant of Rule 2(h): “Any communication by . . . a Party shall be copied to the other Party, the Panel and the Provider, as the case may be” (emphasis added).