Christian Solidarity Worldwide has said last week Vietnamese politicians passed the country's first ever bill which, at face value, could enshrine religious freedom.
However, the exact details of the Law on Belief and Religion have not been made public yet and there are concerns the bill will continue to allow the government to force faith groups to register with them, in order to be allowed to meet together and practice.
The practice is not dissimilar from that of the Chinese government, where Christianity is illegal outside state-monitored and sanctioned churches.
There are also concerns the Vietnamese bill will not get rid of loopholes allowing discrimination and abuse.
CSW's Chief Executive Mervyn Thomas said: "When the possibility of a law on religion was first mentioned, some were hopeful that it would address the obstacles to freedom of religion or belief in the existing regulations.
"Unfortunately, throughout the drafting process, the law continued to focus on the control and management of religious activities, rather than the protection of religious freedom.
"Basic guarantees of the right to freedom of religion or belief must not be undermined by onerous registration requirements, and groups which cannot or choose not to register must not be excluded from the enjoyment of this right."
Meanwhile, Pope Francis welcomed Vietnamese President Tran Dai Quang (main picture) to the Vatican on Wednesday.
According to Catholic Herald, they spoke for 15 minutes privately about "the good relations existing between the Holy See and Vietnam, [which are] supported by a common spirit of dialogue and a constant search for the most appropriate instruments so they can make further progress."
The agency says the conversation also highlighted "the collaboration between the Church and state in various spheres of society" in Vietnam.
The talks are part of ongoing efforts by the Vatican to build a stronger relationship with Vietnam, a country where religious freedom has been suppressed for decades.
