India has published a list which effectively strips about four million people in the north-eastern state of Assam of their citizenship.
The National Register of Citizens (NRC) is a list of people who can prove they came to the state by 24 March 1971, a day before neighbouring Bangladesh declared independence.
India says the process is needed to identify illegal Bangladeshi migrants, reports BBC.
But it has sparked fears of a witch hunt against Assam's ethnic minorities.
Fearing violence, officials say that no-one will face immediate deportation.
They say that a lengthy appeal process will be available to all - even if it means millions of families will live in limbo until they get a final decision on their legal status.
Millions of people fled to neighbouring India after Bangladesh declared itself an independent country from Pakistan on 26 March 1971, sparking a bitter war.
Many of the refugees settled in Assam.
Under the Assam Accord, an agreement signed by then PM Rajiv Gandhi in 1985, all those who cannot prove that they came to the north-eastern state before 24 March 1971 will be deleted from electoral rolls and expelled as they are not considered legitimate citizens.
More than 32 million people submitted documents to the NRC to prove they were citizens, but four million of them have been excluded from the published list.