So what is the base Law which this Amendment Act is amending?

The original Act [Citizenship Act of 1955] states that citizenship may be acquired in India through five methods :

— by birth in India, — by descent, — through registration, — by naturalisation (extended residence in India), — and by incorporation of territory.

And any person deemed as an illegal immigrant will be prohibited from acquiring Indian citizenship under the Citizenship Act of 1955. Section 2(b) of the Citizenship Act of 1955, defines illegal immigrants. Section 3(c) (ii) bars anyone who may be born in India, but one of whose parents is an illegal immigrant, from getting citizenship by birth. Section 5(1) bars Citizenship by registration for illegal migrants. Section 6(1) bars Citizenship by naturalisation for illegal migrants.

And what are the amendments?

The Citizenship (Amendment) Act, 2019 was passed by the Parliament of India on 11 December 2019. This Amendment Act:

Inserted the following provisions in section 2, sub-section (1), after clause (b): Provided that persons belonging to minority communities, namely, Hindus, Sikhs, Buddhists, Jains, Parsis and Christians from Afghanistan, Bangladesh and Pakistan, who have been exempted by the Central Government by or under clause © of sub-section (2) of section 3 of the Passport (Entry into India) Act, 1920 or from the application of the provisions of the Foreigners Act, 1946 or any order made there under, shall not be treated as illegal migrants for the purposes of that Act;

Inserted a new section, 6B, providing further that: On and from the date of commencement of the [Act], any person referred to in the first provision shall be eligible to apply for naturalisation and any proceeding pending against such person in respect of illegal migration or citizenship shall stand abated on conferment of citizenship to him.

Creates a special class of “illegal migrants”, who would no longer be considered as illegal migrants if:

a) they had migrated to India before December 31, 2014,

b) had migrated from Pakistan, Bangladesh, or Afghanistan, and

c) belong to the Hindu, Sikh, Buddhist, Jain, Parsi, or Christian religious communities.

Illegal migrants may be imprisoned or put in detention centres or deported under the Foreigners Act, 1946 and the Passport (Entry into India) Act, 1920. The 1946 and the 1920 Acts empower the central government to regulate the entry, exit and residence of foreigners within India. In 2015 and 2016, the central government issued two notifications exempting certain groups of illegal migrants from provisions of the 1946 and the 1920 Acts. These groups are Hindus, Sikhs, Buddhists, Jains, Parsis and Christians from Afghanistan, Bangladesh and Pakistan, who arrived in India on or before December 31, 2014. This implies that these groups of illegal migrants will not be deported or imprisoned for being in India without valid documents.