It is one of the job assigned to the National Registrar of Births and Death to maintain NRC (National Register of Citizens). But it is so top heavy and expensive work that Central Government has not asked the Registrar to undertake it and neither provided funds for it.
Most of the developed and safe-secure countries face the problem of illegal migrants infiltrating in illegal and clandestine way and settle there. Many migrated for jobs. Centuries back many Indian migrated to Sri Lanka for work in tea gardens and settled there permanently. Now entire north of Sri Lanka is Tamil populated areas. Now Tamils even demanded separate Tamil Elam (Nation) there.
In India large number of Goorkhas migrated to India from Nepal for jobs here and settled permanently. Now they demand ‘separate Gorkhaland’. The America a country of migrants do not went any more migrants to come there for settlement. Large number Mexicans are infiltrating there. The American President Mr.Donald Trump have decided to erect a permanent wall between America and Mexico to check infiltration.
In Assam the problem of infiltration from East Pakistan (now Bangla Desh) particularly of Muslims became so acute that in many Vidhan Sabha and Lok Sabha constituencies they outnumbered original Assam voters. The situation became so explosive that people of Assam put the foot down that no election in Assam till there infiltrators illegal migrants were expelled from Assam. At one time when Lok Sabha general elections were held in India people of Assam not allowed the elections there.
Suring the partition of the country in 1947 into India and Pakistan on Hindu-Muslim the state of Punjab and Bengal were also divided in communal lines. One district of Assam Sylhet was mostly Muslim populated area. Referendum were held to decide whether people of Sylhet would prefer language based decision to stay with Assam or on communal divide on Hindu-Muslim basis would like to joint Bangla speaking East Pakistan.
They preferred Pakistan and only one Sylhet district joined Pakistan. But in Bangla speaking East Pakistan the Muslim of Sylhet found themselves total misfit and disliked. Consequently they in a secret way entered into Assam and Muslim of Assam helped them to come in and settled there. This has created a demographic problem in Assam and the people of Assam revolted and demanded the expulsion of illegal infiltrators from East Pakistan.
This was the compelling situation and ultimately it was decided to prepare an NRC (National Register of Citizens) and expel illegal migrants. This problem is still a burning problem of Assam. The BJP in its election manifesto mentioned that on coming to power it would expel such migrants.
Besides Assam there are large number of Bangla Deshi in Delhi. They have come here during Pakistan crack down during Bangla Desh liberation war but not going back even after the emergence of free and independent Bangla Desh. The Assam is still in turmoil on illegal persons and NRC is prepared to settle the issue permanently.