Not sure to be honest. Most likely because of the very close relations that Baha’i/ the religion has with the state of Israel makes the Iranian government suspicious? It’s not a topic that I have ever paid much attention to but I vaguely remember it being viewed as a political movement not a religion by the state?
Baha’is were persecuted in Iran in the 19th century, before Israel existed. The founder, Baha'u'llah, was exiled to Iraq by the Shah of Iran, and then sent as a prisoner to Palestine by the Ottoman rulers, arriving there in 1868.
Yes, the state-sponsored media in Iran, and Iranian diplomats at the UN, regularly say that the Baha’i Faith is not a religion, but rather a political movement. This is because the constitution guarantees religious freedom in Iran, so they have to define the Baha’i religion as a non-religion. However the reason it is persecuted, is because it IS a religion, founded after Islam, and they believe that "seal of the prophets" means that God's hands are chained forever. And it is a religious community without any clerical class -- scholars in the Baha’i community have no authority, as the community is run by elected "assemblies" of lay people. Those are the main religious reasons for the persecution of the Baha’is. The persecution also entails the confiscation of Baha’i properties, so there is an economic motivation as well.
One of the participants (DigitalUmmah) of the thread commented that due to the close association of the Baha’is with Israel, the Iranian government is suspicious of them. This led another Baha’i (Sen McGlinn) to refute his claim. Another member(basher) brought proofs that the Babism(movement predecessor to Baha’ism) was supported by the then Russian government who were at loggerheads with the Iranian government and therefore the Baha’i cult is no more than a political movement in the garb of religion.