More than 10,000 people have marched in the Taiwanese capital against government attempts to limit the burning of incense and paper money during religious ceremonies.
The government has been pushing to end the practices, along with the lighting of firecrackers, to fight pollution.
The risks include raised levels of PM2.5, benzene and methylbenzene.
The protesters were followers of the Taoist religion. They say the practices are a crucial element of their rituals.
The centre of Taipei was filled with the sounds of clashing cymbals on Sunday as people from about 100 temples took part in the demonstration.
A 59-year-old man, who had travelled from the south of the country and gave his surname as Cheng, told the news agency AFP: "It is very important. Our religion is upheld by the burning of incense."
Joyce Wu, 34, said: "Gods can only feel our worship if we burn incense.
"I grew up in a rural village, how come I'm healthy and not sick? I think cars and factories cause more of a pollution problem."
Last year during a Taoist pilgrimage, government monitors found levels of harmful PM2.5 - particulate matter smaller than 2.5 microns in diameter - had reached more than 60 times the World Health Organization's recommended limit.
The government issued a statement saying it did not wish to ban the practice, but it called on religious groups to "take appropriate measures to reduce potential pollution".
One temple has stopped burning incense, while another has started playing recordings of the sound of firecrackers.