The six men, including Brotherhood for Democracy co-founder and lawyer Nguyen Van Dai, have been charged with "carrying out activities that aim to overthrow the people’s administration".

The Brotherhood for Democracy offers legal assistance to activists in Vietnam and agitates for democracy, greater religious freedoms and human rights in Vietnam.

Vietnam has undergone sweeping social change in recent years, with the size of the middle class growing and the economy increasingly open to the world. It is an increasingly close partner of Australia, the United States and some other ASEAN countries as a strategic balance to China's rise.

However, the communist government retains tight control on the media.

Nguyen and his colleague Le Thu Ha were originally charged with conducting propaganda against the state when arrested back in December 2015.

Just a day before his arrest, Nguyen had met with European Union delegates and participated in a dialogue with Vietnam on human rights. He and Ha were held in detention for 20 months after arrest, without access to legal counsel, according to Human Rights Watch.

The United Nations Working Group on Arbitrary Detention has also condemned Nguyen's treatment at the hands of Vietnamese authorities in a 2017 report. The UN group argued the human rights lawyer and blogger had faced harassment, surveillance, imprisonment and acts of violence for over 10 years for undertaking his work in Vietnam and that his detention was arbitrary.

In July 2017, the charges against Nguyen and Ha were changed to attempting to overthrow the Vietnamese government.

At the same time four other men - Pham Van Troi, Nguyen Trung Ton, Truong Minh Duc and Nguyen Bac - were arrested and the same charge of carrying out activities to overthrow the government was made against them.

Human Rights Watch Asia director Brad Adams condemned the detention and trial of the six men, who are unlikely to escape sanction.

"The only crime that these activists have committed is to campaign tirelessly for democracy and defend victims of human rights abuses,” Adams said.

A broad coalition of other pro-democracy groups including Reporters Sans Frontieres, Viet Tan, Viet Labor Movement and the Nguyen Kim Dien Priests group has also condemned the treatment of the six men.

By James Massola - The Sydney Morning Herald - April 4, 2018