Political parties, students groups and others have been protesting the citizenship bill.
The Congress will issue a three-line whip to its members of Rajya Sabha to vote against the citizenship bill, party general secretary in-charge for Assam Harish Rawat said on Wednesday.
Talking to reporters after separate meetings with Congress chief Rahul Gandhi and Leader of Opposition in Rajya Sabha Ghulam Nabi Azad, Mr Rawat said the party is always concerned about Assam and the Northeast and it will continue to do so.
"As per the directive of the Congress president, the party will issue a three-line whip to its members of Rajya Sabha to vote against the bill," he said, adding it will try to rope in like-minded parties for support against the bill.
A Congress delegation comprising Assam Pradesh Congress Committee president Ripun Bora, leader of Congress legislature party Debabrata Saikia and Mr Rawat besides others on Wednesday met Mr Gandhi and urged him to ensure that the proposed legislation is not passed in Rajya Sabha.
The delegation apprised Mr Gandhi about the prevailing situation in Assam and the Northeast and people's strong sentiment against the bill, which seeks to amend the Citizenship Act 1955 to give Indian nationality to non-Muslims from Pakistan, Bangladesh and Afghanistan.
Terming the bill as "flawed", the Congress had walked out of the debate in Lok Sabha, which passed it during the Winter Session on January 8. The Budget Session of Parliament will begin on Thursday.
The bill provides for according Indian citizenship to Hindus, Jains, Christians, Sikhs, Buddhists and Parsis from Bangladesh, Pakistan and Afghanistan after seven years of residence in India instead of 12 years, which is the norm currently, even if they do not possess any document.
There has been strong opposition in Assam and other Northeastern states against the bill.
Political parties, students groups and others have been protesting on the grounds that the bill seeks to grant nationality to non-Muslims who have come up to December 31, 2014, thereby, increasing the deadline from 1971 as per the Assam Accord.
Also according to the Assam Accord, all illegal immigrants who have come after 1971, irrespective of religion, have to be deported and this bill violates that.
The Asom Gana Parishad (AGP) has quit its alliance with the BJP in Assam protesting against the Narendra Modi government's decision to get Parliament's approval for the bill.
PM Modi had announced that the citizenship bill is an "atonement of the wrong that was done during India's Partition... India will safeguard all who had been victims of the Partition".
Meanwhile, a group of people from Manipur staged protests outside Parliament on Wednesday and set on fire copies of the bill.
The slogan shouting protesters were escorted out of the high-security area by police after about 15 minutes of their protests.