Human Rights Watch is calling on China to ensure that Tibetan filmmaker Dhondup Wangchen receives an open and fair trial and gets to choose his own lawyer.
Police in Xining, in China's Qinghai province, arrested him last year on charges of "inciting separatism" for shooting a documentary about Tibet without permission.
The human rights group said Monday that judicial authorities in Xining replaced Dhondup Wangchen's lawyer with a government-appointed attorney without justification.
The first lawyer had reported that his client was tortured to extract a confession.
Human Rights Watch says a verdict that goes against Dhondup Wangchen under the present circumstances would have no legitimacy.
The right group also says it is gravely concerned about the charge of "inciting separatism." It says the charge violates international human rights standards.
Dhondup Wangchen's film, Leaving Fear Behind
, was based on about 100 interviews with ordinary Tibetans. It was distributed to foreign journalists at last year's Summer Olympics in Beijing.
Tibetan monk Jigme Gyatso, who also took part in making the film, was jailed for seven months. Others involved in the movie say he was beaten, held upside down, and tied to a chair for days while questioned.