The bill is being aggressively opposed by Mulayam Singh Yadav and his Samajwadi Party, mainly because it would upset the party's vote bank of backward castes and Muslims.
The Samajwadi Party has nine Rajya Sabha MPs and they have committed to disrupting the house to prevent a debate and vote on the proposed legislation.
A leader from Mr Yadav's party today demanded in the Rajya Sabha a similar amendment to provide reservation to Muslims The party asked for an urgent debate on this, leading to chaos and an adjournment of the House. "Our stand on the issue remains clear. If there is any community that is suffering it is the Muslims," Mulayam Singh Yadav told reporters outside Parliament.
Mr Yadav is isolated in his opposition to the "quota bill." The main opposition party - the BJP - has agreed to support the bill with some amendments. The government, which is in a minority in the Rajya Sabha, needs the opposition's support to push through the legislation.
The bill's biggest advocate has been Mr Yadav's rival from Uttar Pradesh, Mayawati, who heads the Bahujan Samaj Party (BSP). Her party has 15 Rajya Sabha MPs.
Both Mr Yadav and Mayawati do not participate in the ruling UPA coalition, but provide external support to the minority government; both are crucial to its survival.
Over the weekend, Mr Yadav hinted that he may reconsider his support to Dr Manmohan Singh's government if the "quota bill" is cleared. Today he said, "We will decide whether or not withdraw support when the time comes."
His party has also alleged blackmail - a spokesperson said yesterday that the government is using a CBI investigation against Mr Yadav and his sons for alleged corruption to force the Samajwadi Party to support the quota bill. The party suggested similar pressure tactics had been used to get Mr Yadav to back the contentious reforms in retail which were cleared by Parliament earlier this month and allow the entry of foreign super-markets like Wal-mart.
Article 335 of the Constitution provides that the claims of Scheduled Castes and Tribes have to be balanced with maintaining efficiency in administration. The Bill introduced in the Rajya Sabha last week would override Article 335. The BJP shared it concern over this; the government has reportedly agreed to remove this reference through an official amendment to the Bill.
There was much chaos in the upper house all of last week because of protests by Mayawati and Mr Yadav's parliamentarians. The government is worried about squandering more time because it wants Parliament to take up important reforms in the pension and insurance sectors.