US computer networking giant Cisco Systems has rejected allegations it helped the Chinese government repress the Falun Gong movement.
The spiritual movement is suing Cisco over claims it worked on the "Golden Shield" online censorship network, to help Beijing spy on its citizens.
The law suit says some Falun Gong members had been detained, tortured and even killed as a result of the network.
Falun Gong is banned in China, where the government calls it an evil cult.
The court papers, filed in the US on Monday, allege that Cisco provided networking equipment and technical assistance to Beijing to enable it to create an online "censorship and surveillance network".
It accuses Cisco of aggressively marketing the product, knowing it would be used to crack down on the banned movement.
"Cisco's specific intent to meet the requirements of the Chinese Communist Party's purpose to identify, track and thereby abuse and eliminate Falun Gong practitioners... was expressed in marketing presentations," say the papers.
It alleges Cisco established a subsidiary, China Network Technology Corporation, in Beijing in 1998 to work with the government.
The 52-page suit, brought by the Washington-based Human Rights Law Foundation, names senior Cisco executives, including chief executive John Chambers.
But in a statement issued from its headquarters in San Jose, California, Cisco vowed to "vigorously defend" its operations.
"Cisco does not operate networks in China or elsewhere, nor does Cisco customise our products in any way that would facilitate censorship or repression," the company said.
"Cisco builds equipment to global standards which facilitate free exchange of information, and we sell the same equipment in China that we sell in other nations worldwide in strict compliance with US government regulations."
China's government has invested heavily in controlling what its citizens can access on the internet.
The Golden Shield, also known as the Great Firewall, blocks thousands of websites, including those linked to Falun Gong or the Tibetan spirital leader, the Dalai Lama.
It also filters keyword searches for sensitive topics such as Tibet or Liu Xiaobo, the Nobel prize-winning dissident.