Human Rights Watch on Tuesday called on the Chinese government to set free a group of over 30 labour activists, factory workers, college students and trade union officials detained in a nationwide crackdown launched in mid-2018.
In July, workers at Jasic International, a welding-machinery manufacturer in southern Shenzhen city, staged protests after being fired by their employer while attempting to form an autonomous labour union.
The incident has sparked waves of detentions by the Chinese authorities followed by further activist demonstrations from supporters from across the country, including a group of student activists, who identify as Marxists, from top universities.
Those who have been "arbitrarily detained or forcibly disappeared" should be immediately released, Human Rights Watch said in a statement.
"It's ironic that a self-proclaimed socialist government is cracking down on young Marxists," Yaqiu Wang, New York-based China researcher at Human Rights Watch, said in a statement.
"International labour organizations and universities around the world should show solidarity with Chinese workers and students and speak out against China's suppression of labour activism," Wang said.
China's Ministry of Public Security did not immediately respond to a faxed request for comment.
The stability-obsessed Chinese Communist Party is suspicious of all forms of grassroots organizations that operate beyond its control, especially any that might lead to large-scale protests.
Only worker unions that are registered with the official All-China Federation of Trade Unions are considered legal.
The Jasic workers had been willing to register, but had sought to elect their own union leaders, rather than allowing the company management to choose them.
As a member of the International Labour Organization, China should also be obligated to allow workers to freely associate and collectively bargain, Human Rights Watch said.
Thirty-two individuals remain detained, including labour union officials who helped workers apply to set up their autonomous union, and four have been charged with the crime of "picking quarrels and provoking trouble", according to the Jasic Workers Support Group, a collection of activists.
(With inputs from agencies.)