A bill that grants Indian citizenship to non-Muslim illegal immigrants has been challenged in the Supreme Court.
The Indian Union Muslim League, a political party, has petitioned the court to declare the bill illegal.
The parliament on Wednesday passed the bill which applies to migrants from Afghanistan, Bangladesh and Pakistan.
Critics say the bill is against Muslims, but the ruling Hindu nationalist Bharatiya Janata Party (BJP) has defended it.
The BJP says the Citizenship Amendment Bill (CAB) will give sanctuary to people fleeing religious persecution.
In their petition to the Supreme Court, the Indian Union Muslim League argued that the bill violated articles of equality, fundamental rights and the right to life.
It was passed in the upper house of parliament by 125 votes to 105 on Wednesday. It had already cleared the lower house. It will become a law once the president signs it, which is a formality at this stage.
The CAB has also triggered huge protests in the north-eastern state of Assam, forcing authorities to declare a curfew and shut down internet services.
Prime Minister Narendra Modi sought to reassure people in Assam, telling them they had "nothing to worry" about.
"The Central Government and I are totally committed to constitutionally safeguard the political, linguistic, cultural and land rights of the Assamese people," he tweeted.
However, with internet and mobile services still shut down, correspondents say it is unlikely residents would have been able to read his tweets.
The situation in Assam remains tense, as people defied curfew to protest in the state capital, Guwahati, on Thursday morning. Train services are suspended and some airlines have started offering rescheduling or cancellation fee waivers.
Protests have also taken place in the north-eastern state of Tripura which borders Bangladesh.
BDST: 1441 HRS, DEC 12, 2019