Staff at a small NGO in southern China with links to Hong Kong have been arrested on suspicion of state subversion, as authorities crack down on mainland activists with any possible connections to the protests.

On Monday, lawyers for the three staff members of Changsha Funeng, a public welfare organisation focusing especially on disability rights, said the three had been formally arrested on suspicion of state subversion.

The charge is unusually severe for a group that does not work on overtly political or sensitive issues. Changsha Funeng, a three-person large NGO founded in 2016, describes itself as a “public welfare organisation” advocating for the rights of vulnerable groups and government accountability through disclosure requests.

“It has nothing to do with subverting the government and subverting the political system,” the organisation said in a statement.

In July, police detained the “Changsha Three” as the group is now known. On 22 July, police stormed the home of Cheng Yuan, co-founder of the NGO, in Shenzhen. Cheng’s wife was taken to a neighbourhood committee office with a black hood over her head to face interrogation. The other two were arrested at their homes in Changsha.

According to co-founder Yang Zhanqing, now in the US, the group had set up a company in Hong Kong through which it received funds from overseas. Cheng Yuan, who lived in Shenzhen near China’s border with Hong Kong, regularly traveled to Hong Kong for meetings related to the NGO’s work.

Yang said the group was not affiliated with the protests. On Twitter, Liu Yongze, one of the arrested staffers, retweeted a BBC article about the protests and a comment by another user that read: “Hong Kong people can only fight.” According to Yang, there was no indication the other two were in support of the protests.

Yang said the primary reason for the arrest appears to be the group’s funding, which he said did not violate any laws, but the Hong Kong protests may be another major factor.

“Hong Kong and the anti-extradition movement has had a great impact on the mainland, so there is tighter control on mainland. It’s possible they are arresting people more quickly and putting them under more severe charges,” he said.

The protests, started in June over a bill that would allow extradition to mainland China, have garnered support in some corners of China among liberal pockets of activists, intellectuals, and regular citizens.

Several Chinese activists have been interrogated or detained for expressing support of the protests on social media. A dissident based in the southern province of Guangdong who attended the demonstrations in August was detained for 15 days when he returned. A Wechat user in Shandong province was also reportedly criminally detained for expressing his support of the protesters in Hong Kong in a Wechat group.

“I feel any activists or civil society groups who have somewhat foreign connects are in a dangerous situation,” said Yaqiu Wang, China researcher for Human Rights Watch.

Rights advocates say the space for civil society in China has shrunk dramatically under the leadership of Xi Jinping, who came to power in 2012. Groups that would previously not have been deemed sensitive have been shuttered.

“It’s clear the real motivation is to crack down on independent civil society and rights advocacy,” said Wang. “The prosecutions show that rights advocacy NGOs in China are on the verge of total elimination.”