Decorative 'koteka' have been worn by male inhabitants of New Guinea to cover their manhood for centuries.
The sheath is normally made from a dried out gourd made of a type of pumpkin, and is tied both around the scrotum and the chest to hold it in place.
But last October, Indonesian authorities passed an anti-porn law which empowers authorities to jail people for any sexually suggestive performance.
Now natives may be forced to wear western-style underpants to cover their genitals.
Suroba, a native between 60 and 70 years old who just wears feathers and his penis sheath, is adamant, however, that he will not wear undies. In the 1970s, a Muslim-dominated government tried without success to ban the 'koteka'.
"Back then we wore our traditional clothes, and we are still wearing them today," Suroba said.
He and his fellow tribe members live in the mountain valley of Baliem, which belongs to the Indonesian province of Papua, in the west of New Guinea. Since the Second World War, they have had almost no contact with the outside world and still live in their traditional ways.
But the anti-porn law is highly controversial, with many opponents criticising it for threatening regional cultures.
Even phallic totem poles in Papua or drawings in Balinese temples, which are mainly populated by Hindus, could be threatened by the crackdown. In Bali thousands have already taken to the streets in protest.
Lemok Mabel from the local council for ancient customs in Papua said: "The anti-porn law is a definite threat, as it goes against our cultural values. It violates the rights of the aborigines."
But the regional head of police said: "It is unlikely that we will implement the law, because the people here are too traditional. For them the penis sheath is not pornographic, it is simply a piece of clothing."