While only a small minority of students are involved, they represent a leftist critique of Chinese society that seems to be gaining traction on college campuses, partly because the authorities have been more hesitant to suppress it than other political discussion.

On the Chinese internet, thousands of young people participate in vibrant Maoist and Marxist chat rooms, and some have started leftist news websites, posting commentary on topics like pollution, globalization and economic theory, without much interference by censors, until recently.

This week, school officials harassed young Marxists at a half-dozen universities and prevented some from meeting, activists said. And last year, the police in Guangzhou, the capital of Guangdong Province, arrested Zhang Yunfan, the young leader of a Maoist reading group, accusing him of “gathering a crowd to disturb social order.”

Younger Chinese are often described as apathetic, selfish and obsessed with money. But Eric Fish, a writer who has studied Chinese millennials, said that the generation born after the Tiananmen Square massacre lacks the instinctive fear of authority of older generations.

“They’re more willing to go out on the street and stick their necks out,” he said. “There is not as much appreciation for what could go wrong.”

The dispute in Huizhou began in July, after Jasic Technology, a manufacturer of welding equipment, prevented its workers from forming an independent union. China allows labor organizing only under the auspices of the official, party-controlled All-China Federation of Trade Unions.

The workers said managers had seized control of their branch of the official union. Complaining of being underpaid and treated like slaves, they began to organize a petition before the police intervened and detained several of them.