Religious freedom in Vietnam is at risk of deteriorating under the government's new Law on Belief and Religion, a senior bishop told officials on Monday.

Bishop Peter Nguyen Van Kham, secretary general of the Catholic Bishops' Conference of Vietnam, was speaking at a meeting between government officials and representatives from religious groups, the National Catholic Reporter reports.

This law, which passed on November 18 and will take effect in 2018, "fails to properly care about and satisfy people's needs of religious activities," Kham said.

"From our views, some negative issues still remain in relationships between the government and religions."

Christian persecution charity Christian Solidarity Worldwide (CSW) previously warned that the new legislation does not conform to international standards on freedom of religion or belief.

"The text of the law has been revised numerous times. Some improvements to the draft were made during the revision process, possibly in response to the feedback offered by religious communities. However, these improvements, and the inclusion of basic guarantees of the right to freedom of religion or belief, were undermined by onerous registration requirements and excessive State interference in the internal affairs of religious organisations," CSW said.

Vietnam's constitution guarantees freedom of religion in principle, but the Communist government tightly controls independent religious practice. According to the US Commission on International Religious Freedom (USCIRF), it represses "individuals and religious groups it views as challenging its authority", including independent Buddhists, Hoa Hao, Cao Dai, and Christians.

A number of advocates for religious freedom remain imprisoned in the country and authorities have "moved decisively" in recent years to restrict freedom of expression and religion even further, the USCIRF says. Religious groups have to formally register with the government, but are routinely denied. The Hmong Protestants have experienced particular persecution in the last few years, and Vietnam has been named a 'country of particular concern' every year by the USCIRF since 2001.

CSW has urged the Vietnamese government to ensure that registration is not a pre-requisite for the exercise of freedom of religion or belief.

The UN special rapporteur on freedom of religion or belief previously made a similar request.

Of the 93.4 million Vietnamese, more than half identifies with Buddhism. Roman Catholics make up seven per cent, Cao Dai between 2.5 and four per cent; Hoa Hao, 1.5 to three per cent; and Protestants, one to two per cent.