The lines between politics and religion are often blurred in Iran. While its president is democratically elected, its supreme leader is a Muslim cleric. Islam is the official religion, with Zoroastrianism, Judaism, and Christianity officially recognized as minority religions.
The Baha'i Faith, however, has no such recognition even though it is the largest minority religion in Iran. Baha'is find themselves barred from many opportunities including higher education, and they are prone to harassment and execution. The persecution of Baha'is in Iran can be traced to several different reasons.
Not "People of the Book"
The Koran commands Muslims to respect the People of the Book, namely Christians and Jews, with whom Muslims share their mythology. Muslims also commonly include Zoroastrians in that category, for while they do not officially share holy texts, Zoroastrianism does share many similarities, including monotheism, the belief in an evil spirit roughly equivalent to Satan, a Final Judgment, and the moral judgment of the soul.
While the Baha'i recognize prophets from all four religions (along with those of others) and are monotheists, Muslims have never considered them People of the Book.
Islamic Heresy
The Baha'i Faith is considered an Islamic heresy in Iran. While Zoroastrianism, Judaism, and Christianity all predate Islam and thus can be seen as providing a foundation for the more perfected religion of Islam, the Baha'is developed in the 19th century out of Shi'a Islam. Thus, it is seen as an erroneous deviation from the true faith.
Moreover, apostasy is a serious offence within Islam, and the original Baha'is and Babis were previously Muslims.
Mohammed Not the Final Prophet
Particularly heretical to Muslims is the Baha'i belief that Mohammad, along with Moses, Jesus, Zoroaster and others, is one of many Manifestations of God and that others have come after Mohammad and will continue to appear in perpetuity. According to Islam, Mohammad was a mortal man called by God to be the greatest and last of his prophets.
Politics vs. Religion
Iran's leaders have repeatedly stated that they consider Baha'is to be part of a political group rather than a religious one and thus they are under no obligation to grant religious tolerance toward them. Baha'is do support and encourage a variety of social causes and have visions of political unity across the world, but they do it for the same reason that Muslims give alms: they are following what the consider to be the will of God.Relationship with Israel
The Baha'i Faith is today headquartered in Haifa, Israel and generally has good relations with the Israelis. As such, Iran opinion of Baha'is can ebb and flow alongside their opinion of Israel. Baha'is have even been arrested as or suspected of being spies (for Israel, the United States, Great Britain and other countries).Threat to Clerical Power
Baha'is have no priests and place the responsibility for spiritual interpretation entirely in the hands of individuals. Many of their historical texts are critical of traditional Muslim clerics and the power they hold over the populace.Historical Roots
The Baha'i Faith grew out of the Babi Faith, which in turn developed out of Shi'a Islam. The Bab was understood by many to be the Hidden Imam and the Mahdi, an Islamic redeemer figure who will return as part of the end of days. There have been many Muslims who have previously associated themselves with the Mahdi for political purposes, hoping to overthrow the established order in the name of Allah.
Read more: The Hidden Imam, the Mahdi, and Baha'i roots in Shi'a Islam