A Chinese businesswoman was sentenced to three years’ jail on Tuesday, according to her supporters, after she spoke out in defence of dissident law professor Xu Zhangrun, who has openly criticised the Communist Party and President Xi Jinping.

Geng Xiaonan, 46, and her husband Qin Zhen, as well as employees of her private publishing company, stood trial at the Haidian District People’s Court in Beijing after the couple were detained in September and investigated for “illegal business operations”.

There was a heavy police presence outside the court and supporters said they were barred from entering. Friends including Xu and activists Ji Feng and Yan Zhengxue were stopped by the authorities from leaving their homes to attend the hearing.

The trial was broadcast live by the Haidian court but footage was taken down from its website after it was viewed more than 80,000 times and it did not release a statement on the case.

After asking the court to disregard her legal defence, Geng pleaded guilty to charges including conducting illegal business activities, according to a video of the trial that was captured and posted online.

Xu Zhangrun was said to have been stopped from leaving his home on Tuesday.

In pleading guilty, Geng asked the court for leniency in the cases of her husband and staff, saying they had been “forced to carry out orders from their boss”. She also contradicted her legal defence and claimed to have been “the sole proprietor and decision maker” of the publishing company since 2001.

“I would really appreciate it if the court would be lenient on them and target all of the sentencing burden on me alone,” Geng said.

She also asked the court to consider giving her a lighter sentence on humanitarian grounds since she is the only child of, and supports, her disabled war veteran father who lives alone.

Qin, Geng’s husband, was sentenced to 2½ years in prison, suspended for three years.

A number of Geng’s supporters, including prominent liberal intellectual Guo Yuhua, went to the Haidian court but were blocked from entering. Witnesses said more than a dozen police vehicles were parked outside the court, and Geng’s lawyers had been warned not to speak to the media.

Dissident Ji said he had been told by state security personnel on Monday evening to stay at home the next day. “Two officers came to my house in the morning and stopped me from leaving. The same thing happened to Xu Zhangrun,” Ji said by phone.

He said Geng had been indicted over illegal business activities involving 200,000 copies of mostly cookery books for which the full publishing rights had not been obtained.

“‘Illegal business activities’ is just an alternative charge to ‘inciting state subversion’ when it comes to entrepreneurs who are critical of China’s political ecology,” Ji said. “The purpose is to intimidate, silence and cut off all social networks they have with political dissidents in a bid to isolate them.”

Geng, who is also an art curator and film producer, was detained, along with her husband, two months after she had spoken out in support of Xu. He had been detained by police for “patronising prostitutes” during a trip which Geng organised for a group of academics including Xu to the southwestern city of Chengdu last year.

Xu, who has since been released but cannot leave Beijing, denies the charges and has hired lawyers to clear his name. After he was detained, Xu was sacked by Tsinghua University in Beijing where he had taught law for 20 years. The university also accused Xu of publishing articles since mid-2018 that “seriously violated” its code of conduct.

Xu, 57, has written a series of articles criticising the authorities in recent years, taking aim at Communist Party leaders over the decision to remove the two-term limit on the presidency – allowing Xi to remain as president after 2023 – and the handling of the coronavirus pandemic.