The category of‘Overseas Citizens of India’ was entered in the Citizenship Act of India through an amendment in the year :

The category of 'Overseas Citizen of India' (OCI) was introduced into the Citizenship Act, 1955, through the Citizenship (Amendment) Act, 2003. This amendment followed the recommendations of the High-Level Committee on the Indian Diaspora, chaired by L.M. Singhvi, which submitted its report in 2002. The 2003 Act made provisions for the acquisition of OCI status by Persons of Indian Origin (PIOs) belonging to 16 specified countries, excluding Pakistan and Bangladesh. While the scheme was later expanded by the Citizenship (Amendment) Act, 2005, to cover PIOs of all countries (except Pakistan and Bangladesh) and the program was formally launched in early 2006, the legal entry of the OCI category into the principal Act occurred in 2003 [1]. The 2003 amendment also introduced the definition of 'illegal migrant' and modified citizenship by birth.

Sources

1. [1] Introduction to the Constitution of India, D. D. Basu (26th ed.). > Chapter 7: CITIZENSHIP > Concept of Overseas Citizens of India. > p. 86