Some decades ago a rumor started spreading that Iranian Kohanim were not actually Kohanim; rather, the uneducated Persian Jews would often “volunteer” to be Kohanim for some period of time as a token of thanks to Hashem for some personal salvation. Although the Iranian rabbis who had been on the ground in Iran in the 20th century penned a letter testifying that they never witnessed this phenomenon, the damage was already done, and some Poskim even till today will consider the possibility in cases of Jewish status determination for Kohanim from Iran.
Rav Djavaheri and Rav Eliyahu Bar Shalom, the chief rabbi of Bat Yam, published an article and rebuttal in the HaMashbir journal refuting and defending these rumors and their halachic value.
You can read the article below and listen to the shiur here: The Priestly Republic of Iran – Defending the Lineage of Persian Kohanim.