A letter has been sent to Prime Minister Narendra Modi seeking his intervention as non-payment of penalty would entail jail terms for them, he said.
Five fishermen, four belonging to fishing hamlets here and one from neighbouring Thiruvananthapuram in Kerala, were detained by Iranian authorities on September 22 for allegedly fishing in their territory. They were employed with a Qatar fishing firm.
"The five fishermen have been fined Rs.5.5 lakh (value in Indian currency). The owner of the Iranian fishing firm Yousuf Ali Binali, a Qatari national, has declined to pay penalty to free them," President, Tamil Nadu Fishermen Development Trust, P Justin Antony told PTI.
"Tamil Nadu fishermen found 20 more Indian detainees there. In all, 25 Indian fishermen are now in Iranian custody," he said.
"The firm that employed these 20 fishermen appear to have undertaken to pay fine and get them released," he said.
The families of the detained fishermen, Sasi Louis, Arokiam, Anthonis, Thadeuse (Kerala) and Antony have already appealed to the authorities to secure their release.