The opposition had earlier warned that it will challenge the bill in Supreme Court.
Even as protests against the Citizenship (Amendment) Bill raged in the Northeast, the Congress today announced that it will challenge the "discriminatory and unconstitutional" nature of the legislation in the Supreme Court.
The bill, which aims to make it easier for non-Muslim migrants from three neighbouring countries to get Indian citizenship, has been criticised by rights groups and opposition parties as being discriminatory on the basis of religion and violating the constitutional right to equality.
In its petition, the Congress is likely to describe the legislation as a flagrant violation of Article 14 and lodge a strong objection against the government's plan to exclude a section of the immigrants on the the basis of their religion. "We believe that the bill is unconstitutional, and the court will decide. It is true that persecutions have happened (in neighbouring countries), and the Congress has always opened its arms to such people. But the peculiar thing about this case is how it relates specifically to Assam. This bill would not have come if everybody excluded from Assam's National Register of Citizens (NRC) list were Muslim," Kapil Sibal, senior advocate and party leader, told NDTV. He was referring to the 19 lakh people excluded from the NRC list published in the state earlier this year, a substantial number of whom were believed to be Hindus.
Mr Sibal, however, did not elaborate on how his party plans to proceed with its legal challenge.
The Congress' decision to approach the Supreme Court against the legislation doesn't come as a surprise, given that many of its leaders had already warned the centre that it will not survive judicial scrutiny. "I am convinced that this bill is an assault on the very foundation of the Constitution of India. It hurts the very soul of the Constitution of India. It goes against the very preamble of the Constitution," said party MP Anand Sharma during the heated debate that preceded the passage of the bill in the Rajya Sabha.
The opposition party also expressed concern over the likely impact of the bill on the Northeast, which has been gripped by violence since Wednesday. "CAB is an attempt by the Modi-Shah government to ethnically cleanse the North East. It is a criminal attack on the North East, their way of life and the idea of India. I stand in solidarity with the people of the North East and am at their service," Congress leader Rahul Gandhi tweeted ahead of the bill's passage.
The ruling BJP had managed to pass the bill in the Rajya Sabha on Wednesday night, with 125 voting for it and 99 against. The legislation will become law after it acquires President Ram Nath Kovind's assent.
The Kerala-based Indian Union Muslim League had also challenged the bill in the Supreme Court earlier in the day, asking for it to be struck down immediately.