A joint initiative by 14 Vietnamese and international organisations, including Christian Solidarity Worldwide (CSW) has called for the release of 165 people arrested for their religious or political beliefs.
However, according to the advocacy group, the challenges of obtaining information about prisoners in the country mean that the real number is likely to be higher.
CSW's Chief Executive Mervyn Thomas welcomed the initiative and said: "Our research consistently finds that Christians and other religious communities in Vietnam continue to experience violations of their right to freedom of religion or belief.
"In particular, Christians from indigenous people groups suffer a double discrimination as both religious and ethnic minorities."
The NOW! Campaign has urged the government of Vietnam to immediately release "all prisoners of conscience", which is "anyone who has been arrested for his/her political, religious or conscientiously held beliefs, ethnic origin, sex, colour, language, national or social origin, economic status, birth, sexual orientation or other status, who has not used violence or advocated violence or hatred".
Thomas explained the vital role prisoners of conscience play in the Southeast Asian country.
He said: "In addition, a significant number of human rights defenders in Vietnam belong to religious communities.
"These individuals play a vital role in promoting the right to freedom of religion or belief.
"We call on the Vietnamese government to release all prisoners of conscience in Vietnam, and to uphold the right to freedom of religion for all."
The charity said in a statement that it continues to receive numerous reports of violations against such groups, in particular those located in remote parts of the country.
Violations include harassment, forced evictions, beatings, torture, and imprisonment.