The ultimatum issued by the Hindu extremists has forced some Christians to abandon their religion altogether, according to the Global Council of Indian Christians (GCIC), a Bangalore-based Christian advocacy group.
"I am forced to convert to Hinduism whether I like or dislike; I cannot say further and my life is in danger," Promond Digal, 32, from the violence-hit Kandhamal district, told GCIC.
A clash over a decorative arch for the Christmas celebrations on December 24 led to large-scale communal violence and attacks against churches throughout the district. Four people were confirmed dead while, 95 churches and 730 houses were burnt down or destroyed after several days of violence, according to the All India Christian Council (AICC).
Earlier this month, a fact-finding team from the National Commission for Minorities (NCM) of India accused Hindu fundamentalists of perpetrating "organised and pre-planned attacks" against the Christian community.
The commission pointed to the possible involvement of organisations including Vishwa Hindu Parishad (World Hindu Coucil), Rashtriya Swayamsevak Sangh (National Volunteers' Organization or RSS) and their affiliates.
AICC and GCIC, on the other hand, have openly accused the Hindu organisations of being responsible for the attacks on Christians.
Furthermore, although the anti-Christian violence has apparently subsided, "fundamentalists are going to individual families with guns and threatening them to become Hindus," GCIC said.
Christians who have converted to Hinduism expressed their helplessness about changing their religion.
"Fundamentalists came and threatened me and my family and said if you do not change your religion prepare to leave the village or die, there was no other way than to accept Hinduism," said B Digal, 60, from Gochhapada village.
Samonary Digal, a Catholic in the Kandhamal district, similarly reported how the members of the RSS "warned me to prepare to die or to leave the place if you do not become Hindu".
"Finally I had to accept what they say," he admitted
According to social worker R Nayak, 25 Dalit families of Mahasingh village were converted to Hinduism on December 25.
"They were forced to drink mixed water of cow dung, ghee and perform the Hindu ritual," he reported
"They live under threat and convert then. They live under danger and panic."
Another forced convert, who did not want to disclose his name, said he was told, "If you cannot be a Hindu, we will finish you off and set fire your entire house."
However, he added, "I and my family have left the faith but God will remain with us."
Relief organisations, including Christian NGOs, are not yet allowed to go into the violence-struck districts. Food distribution from the state government, meanwhile, seems to be improving, GCIC reported.
Orissa state is the site of the 1999 slaying of Australian missionary Graham Staines and his sons - Philip, 10, and Timothy, 8 - who were burned to death as they slept inside their vehicle after a Bible study class. It is the only Indian state that has a law requiring people to obtain police permission before they change their religion - a move designed to counter missionary work.