The bill seeks to give citizenship to Buddhists, Christians, Hindus, Jains, Parsis and Sikhs, who fled Afghanistan, Bangladesh and Pakistan before 2015
India's ruling Hindu nationalists pushed for final parliamentary approval on Wednesday for a law that critics say undermines the country's secular constitution by granting citizenship to non-Muslim minorities from three neighbouring countries.
Having obtained assent from the lower house of parliament a day earlier, Home Minister Amit Shah tabled the Citizenship Amendment Bill in the upper house and a vote is expected late on Wednesday.
Opposition parties, minority groups, academics and a US federal panel have contested the proposed law, which would for the first time provide a legal route to Indian citizenship based on religion, calling it discriminatory against Muslims.
The bill seeks to give citizenship to Buddhists, Christians, Hindus, Jains, Parsis and Sikhs, who fled Afghanistan, Bangladesh and Pakistan before 2015.
Protests against the bill turned violent on Wednesday in India's ethnically diverse northeastern region, with the army deploying troops in Tripura state and putting reinforcements on standby in neighbouring Assam, where police battled thousands of protesters.
Police in Assam's main city of Guwahati used water cannons and tear gas as they clashed with protesters, who had blocked roads with flaming tyres.
"The bill will take away our rights, language and culture with millions of Bangladeshis getting citizenship," said Gitimoni Dutta, a college student at the protest.
Despite Shah's assurances that safeguards will be put in place, people in Assam and surrounding states fear an influx of settlers could lead to a competition for land and upset the region's demographic balance.
In northern India, thousands of students at Aligarh Muslim University began a hunger strike in protest.
Some opposition Muslim politicians have argued that the bill is targeted against the community, accusing the government of Prime Minister Narendra Modi for trying to render them "stateless."
The US Commission on International Religious Freedom said on Monday that Washington should consider sanctions against Shah, a close associate of Modi, if India adopts the legislation.
Introducing the bill in the upper house, Shah defended his government's move, saying the new law only sought to help minorities persecuted in Muslim-majority countries contiguous with India.
"For India's Muslims, there is nothing to worry about, nothing to debate. They are citizens, and will remain citizens," Shah said.
Unlike the lower house, where Modi's Bharatiya Janata Party (BJP) has a clear majority, the ruling party will likely find it more challenging to push the bill through the upper house, as it is unclear whether it can garner enough support from regional parties.