On Monday, 100 scientists and scholars at institutions in India and abroad published a joint letter expressing their "dismay" at the legislation
India's parliament saw raucous scenes on Monday and protests raged in the north-east of the country as MPs debated legislation that stands to give citizenship to religious minorities from neighbouring countries, but not Muslims.
To Muslim organisations, rights groups and others, the bill forms part of Prime Minister Narendra Modi's agenda -- which he denies -- of marginalizing India's 200-million-strong Islamic minority.
The Citizenship Amendment Bill provides that Hindus, Sikhs, Buddhists, Jains, Parsis, and Christians fleeing persecution in Muslim-majority Afghanistan, Bangladesh and Pakistan can be granted citizenship.
Modi's government had tried to bring in the contentious legislation during its first term but the bill could not pass the upper house where the Bharatiya Janata Party (BJP) and its allies lack a majority.
Shashi Tharoor, a member of the opposition Congress party, told parliament amid angry exchanges that the bill "infringes upon the principle of equality before law" guaranteed to all persons, including non-citizens.
The bill seeks to amend the Citizenship Act of 1955 which prohibits illegal migrants from applying for Indian citizenship.
Under Modi, the Islamic-sounding names of several cities have been changed, while some school textbooks have been altered to downplay Muslims' contributions to India.
In August his administration rescinded the partial autonomy of Jammu and Kashmir, India's only Muslim-majority state, and split it into two.
On Monday, 100 scientists and scholars at institutions in India and abroad published a joint letter expressing their "dismay" at the legislation.
They said that enshrined in India's constitution is the notion of treating all faiths equally.
But Modi's "proposed bill would mark a radical break with this history and would be inconsistent with the basic structure of the constitution".
The letter said such a careful exclusion of Muslims would "greatly strain" India's pluralism.
The government has defended the bill, saying it was only aimed at flushing out infiltrators, and that Muslims did not face persecution in the three neighbouring countries.
"This bill is not even 0.001% against minorities. It is against infiltrators," Home Minister Amit Shah said in parliament's lower house.
Recently he has also proposed a "national register of citizens" that would see "each and every infiltrator identified and expelled" from India by 2024.
The citizenship bill has led to protests in India's northeastern states where residents are unhappy about an influx of Hindus from neighbouring Bangladesh.
In Guwahati in Assam state protestors set fire to tyres, while tribal groups staged protests in Tripura.
On Monday, prominent political groups opposing the bill called for a complete shutdown across all the states in the northeast on Tuesday.