Ming Seng, 78, and his fellow monk Eta Toul, 18, performed a 20-minute water blessing for workers in Phnom Penh before they were detained by police.
"I felt scared and wondered why they were questioning me like this. I was just blessing people in the usual Buddhist way," Seng told The Phnom Penh Post.
Both monks were released after 20 minutes, but the 2,000 striking workers were outraged at the action, and many moved to the police station to protest, the Post reported.
Cambodia's Buddhist superiors have said they don't want their monks involved in political dissent or protests, but many believe Buddhism is about human rights, and that monks should help the oppressed.
"At the moment, many poor communities are vulnerable and being moved by the rich far away from our homes," Venerable Thorn Vandong, executive director and founder of Buddhism for Social Development Action said. "We have to help these people."