Christian human rights lawyer and pro-democracy activist Nguyen Van Dai, as well as pastor and activist Nguyen Trung Ton are included in the group.
If convicted under Article 79 of the Vietnamese penal code, they could receive maximum penalty of capital punishment.
According to religious freedom charity Christian Solidarity Worldwide (CSW), Dai has provided legal advice and representation to victims of human rights abuses, including religious minorities, across Vietnam. He has been repeatedly harassed and attacked by authorities and served four years in prison for doing so.
CSW has been advocating on behalf of Christian human rights lawyer #NguyenVanDai since 2007, due to the discrimination, harassment and violence that he has faced a the hands of the #Vietnamese government for his work. pic.twitter.com/KCTbAfOS5H— CSW_UK (@CSW_UK) April 4, 2018
The charity added that Pastor Ton has advocated for the right to freedom of religion or belief and spoken out against social injustices.
He and his family experienced first-hand the authorities' persecution of religious minorities when they and their church members were repeatedly and violently attacked by local authorities and policemen.
Pastor Ton was sentenced to two years' imprisonment and two years' house arrest. After his release in 2013 he joined the Interfaith Council of Vietnam, which advocates for religious freedom. He was arrested again on 30 July 2017.
Legal expert Nguyen Bac Truyen, activist Pham Van Troi and citizen journalist Truong Minh Duc will also stand trial this week.
CSW'S chief executive Mervyn Thomas said Christians in Vietnam constantly have their right to freedom of religion violated and added that the work these activists have done have been paramount to defending the rights of citizens.
"Nguyen Van Dai, Nguyen Trung Ton and Nguyen Bac Truyen are three of the most courageous defenders of religious freedom in Vietnam today: they have risked their personal safety and their freedom to stand up for the rights of the most vulnerable in society, and have been beaten, harassed and imprisoned for doing so," Thomas said.
"We call on the Vietnamese government to release immediately and unconditionally the six defendants and all those detained in connection with their peaceful defence of human rights, in line with the provisions of the International Covenant on Civil and Political Rights, to which Vietnam is a party."
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