Mr Dinh has defended pro-democracy activists and bloggers
Vietnamese authorities have charged a leading human rights lawyer with working to overthrow the state - a more serious charge than he initially faced.
Le Cong Dinh, arrested in June, was first accused of a lesser charge of spreading anti-government propaganda.
He had strongly advocated free speech while defending two other dissident lawyers two years ago.
Mr Dinh is expected to go on trial in the next few weeks, alongside three other dissidents.
Western diplomats and human rights groups have expressed concern about Mr Dinh's case.
The new prosecution charges, announced on Tuesday and reported by state media on Wednesday, are against Mr Dinh, Internet activist Nguyen Tien Trung, and fellow defendants Tran Huynh Duy Thuc and Le Thang Long.
Mr Dinh, Mr Trung and Mr Thuc face a minimum of 12 years in prison or even the death penalty, the Thanh Nien newspaper reported.
The fourth suspect, Le Thang Long, was also charged with subversive activities but as an accomplice, which would lead to a maximum of 15 years in jail, the newspaper reported.
According to Thanh Nien, prosecutors have described that case against Mr Dinh and his associates as a "particularly serious violation of national security".
The paper quoted the indictment as saying Mr Dinh and his associates "colluded with Vietnamese reactionary groups and hostile forces in exile" to form a political organisation "aimed at overthrowing the people's government through non-violent means".
The defendants have also been accused of links with the Democratic Party of Vietnam, a group earlier linked to the Vietnamese Communist Party but now banned.
A fifth defendant, Tran Anh Kim, is to be tried separately in the northern province of Thai Binh.
The rights group Amnesty International has called for the release of the men, describing them as "prisoners of conscience".
Mr Dinh was also accused of participating in a three-day training course for non-violent struggle organised by Viet Tan, a California-based pro-democracy group that Vietnam considers a terrorist organisation.
The US has said there is no evidence to suggest that Viet Tan is a terrorist group.
Mr Dinh studied law at Tulane University in the United States on a Fulbright scholarship and has served as vice chairman of the Ho Chi Minh City bar association.