Beijing (CNN) China's universities have always been a breeding ground for political activism, from the May Fourth Movement which helped lead to the Communist revolution, to the 1989 pro-democracy protests which sought to reform it.

Today, however, China's leaders have no intention of allowing students to challenge them, as a months-long crackdown against a Marxist university group demonstrates.

This week, footage reportedly emerged of apparently staged confessions by a number of prominent student activists, including Yue Xin and Shen Mengyu, both of whom disappeared late last year while protesting to support striking workers in Shenzhen

The 30-minute video purportedly shows four recent graduates including Yue and Shen disavow their previous behavior, and apologize for criticizing the ruling Communist Party.

CNN has not independently confirmed the contents of the video. A source who had seen it described it to CNN, the source's account matched independent descriptions of the video shared online.

In the video, Yue -- who published an open letter in July 2018 calling for students at universities across China to support the workers at Shenzhen's Jasic Technology -- is alleged to say she has been influenced by "radical leftists" and now realizes her behavior is "illegal."

The video also allegedly shows Shen saying she had tried to overthrow the Communist Party and the government. She allegedly expresses regret that her behavior has resulted in "foreign forces" attacking China's government.

Both women disappeared last summer after traveling to Shenzhen to support the Jasic workers.

In a statement , the Jasic Workers Support Group condemned the confession video as a "ridiculous smear," and accused the authorities of using it to "threaten and divide" those organizing on behalf of workers.

Shen and Yue could not be reached for comment.

A group of students hold up signs as they protest against the change in a student-run Marxist group's leadership at Peking University in Beijing on December 28, 2018.

Students described as looking 'dull and glassy'

Following Yue's disappearance, a group of alumni and students at Peking University -- where Yue was a recent graduate -- set up the "Finding Yue Movement" to lobby for the her release. One of the organizers of that group, Zhang Shengye, reportedly disappeared soon after.

At the time, a student at PKU told CNN the situation on campus was like "under the white terror," referring to a period during the 1920s when leftists were violently suppressed by the Nationalist government ahead of the Chinese Civil War.

Another student, Qiu Zhanxuan, who headed PKU's Marxist Society, was bundled into a car by suspected plainclothes policemen in late December on his way to celebrations for the birthday of former Chinese leader Mao Zedong

Despite this, however, students at the university have continued to organize, protesting on campus in late December when the school forced a takeover of the the previously largely-independent Marxist Society. Protesters were dragged into classrooms and detained there overnight they said. They were released the following morning.

Following their detention, selected students were reportedly shown the confession video featuring the four young activists, including Yue and Shen. Sources told CNN that the around 20 students were forced by police to watch the video. Some parents and teachers were also reportedly forced to watch the video, as were students at Renmin University, another prestigious Beijing school.

A source that watched the confession video described to CNN that the four graduates on screen looked dull and glassy, "apart from Yue Xin looked relatively sane, the other three people looked like they had totally changed into another person, maybe it's because their toughness and had suffered more." The source declined to be named due to the sensitivity of this matter.

Representatives for PKU, Renmin University and China's Ministry of Public Security did not immediately respond to a request for comment.

Peking University in Beijing, seen in the snow.

Shrinking space for dissent

The continued heavy-handed crackdown against student protesters suggests the authorities remain concerned about the effectiveness of criticism from the left.

Eli Friedman, an associate professor of international and comparative labor at Cornell University who has been in contact with the Chinese student groups supporting workers' rights, said the crackdown would only serve to undermine the party's legitimacy.

"What is socialism if not standing with the workers?" he told CNN in November

He said the crackdown was a "very conscious strategy on the part of the state to close a space for academic freedom."

In a speech to Party cadres Monday, Chinese President Xi Jinping said all levels of government needed to "ensure China's political security."

"We need to continue to consolidate and strengthen mainstream public opinion and increase public opinion guidance," Xi said, adding it was particularly important to "guide the Chinese youth to form a correct view of world, life and values."