Amnesty International is demanding Vietnam immediately and unconditionally free environmental activist Le Dinh Luong, who is scheduled to go on trial Thursday.
Le Dinh Luong has been accused of taking part in activities aimed at "overthrowing the state" — charges Amnesty says are political.
"For peacefully campaigning on behalf of fishermen affected by an environmental disaster, Le Dinh Luong could face a life sentence or even the death penalty," Amnesty's Clare Algar said Wednesday.
She calls on Vietnam to drop the charges, saying Le Dinh Luong was denied access to a lawyer only until a few weeks ago, leaving doubts whether he can get a fair trial.
Le Dinh Luong is a long-time free speech activist. He helped lead the fight for compensation for fishermen whose livelihoods were ruined when a Taiwanese-owned steel plant dumped toxic waste in Vietnamese waterways in 2016, killing massive numbers of fish.
The company admitted responsibility only after protests erupted across Vietnam.
Authorities arrested 40 demonstrators while others fled the country. Le Dinh Luong was jailed last year and denied access to any visitors or a lawyer until last month.