The Jasic Workers Solidarity group says police "violently arrested" three of its members.
Chinese police have detained three more labour rights supporters, an activist group said, in a crackdown on a workers movement that drew in students fired by an official call to return to Marxism.
The Jasic Workers Solidarity group said police in the central city of Wuhan "violently arrested" three of its members on Sunday, with one of them pinned to the ground by at least three officers.
That follows Friday's police raids on the homes of at least 10 activists who were detained in Beijing, Shanghai and Guangzhou, including students from some of China's top universities, the group had said earlier.
Jasic Workers Solidarity rose to prominence this summer when student activists threw support behind efforts to form a workers' union at Chinese welding machinery company Jasic Technology in southern Guangdong province to agitate for better working conditions.
That triggered police raids in August that swept up a number of the group's members and student activists, according to Jasic Workers Solidarity, which said some of those detained were beaten.
The three latest reported detentions in Wuhan included a member of the solidarity group and a graduate of Renmin University, one of China's top schools.
A video which accompanied the labour group's statement showed a person held to the ground by several men dressed in black.
AFP could not independently verify the group's claims or the video.
Chinese police have not responded to requests for comment.
Peking University confirmed to AFP that graduate student Zhang Shengye was among those taken away on Friday, but declined to give further details.
Another Peking University student, Yu Tianfu - who said he had witnessed Zhang's arrest and was himself tackled Friday night by masked men in black - has subsequently gone missing and his account on Chinese social media deactivated, classmates posted on social media.
Rights campaigners told AFP Tuesday that five activists in Guangzhou who had been detained last week have now been released.
Activism at China's top universities has surged in recent years as the government of President Xi Jinping has advocated renewed study of Marxism and young college students rally behind labour rights and other leftist causes.
But that has also put the students in the cross-hairs of authorities who have waged a broad clampdown on dissent.
Yue Xin, a Peking University student who co-authored a petition demanding details on alleged sexual abuse at the school, has not been heard from since she was detained in the August raids.
Two students from Renmin University and Peking University were also detained for several hours Thursday after taking photos at an Apple store in Beijing, while protesting the alleged exploitation of workers at a factory of one of the US company's suppliers in southwestern China.
"These latest detentions and disappearances will only make matters worse in the long run because the authorities have so far failed to address the issues that gave rise to the protests in the first place," said Geoffrey Crothall, communications director for Hong Kong-based China Labour Bulletin, which supports Chinese workers' rights.
Those issues include poor factory pay and working conditions, and the right to unionise, he said.