Here are 10 facts in this big story:
The Government has requested the Speaker to skip Zero Hour today to start the debate at noon, immediately after Question Hour. After the debate, the 250-odd clauses in the bills will be voted on one by one and the process will take time.
Arun Jaitley has said the government wants to take the bills through Parliament with the consensus of all parties as was witnessed when the government and opposition came together in August last year to pass the bill that amended the Constitution to facilitate the launch of GST.
Mr Jaitley briefed BJP members of Parliament at a meeting also attended by Prime Minister Narendra Modi yesterday. He explained the four bills and how they would help set up a one-nation one-tax regime.
The Congress says the bills in their current form are "not acceptable" and its speakers today will raise their concerns and demand changes. But senior leaders are also wary of being seen as stalling the biggest tax reform since Independence and have suggested treading cautiously.
Congress vice president Rahul Gandhi told his party's lawmakers at a meeting on Tuesday that they should play the role of a constructive opposition. He also told them to raise the issue of the farmers' distress and press for a farm loan waiver in Parliament.
The government, which has a big majority in the Lok Sabha, expects to get the lower house's approval for the GST bills with ease in the vote at the end of today's debate. Any amendments sought by the Congress or other opposition parties will also be voted on.
The bills will then go to the Rajya Sabha or upper house for discussion. Because they are all "money bills", the Rajya Sabha can suggest changes which will be taken back to the Lok Sabha. The Lok Sabha can choose to accept or reject the proposals.
The government has to ensure that this entire process is wrapped up by April 12, when the Budget session on Parliament ends, to be able to to meet the July 1 launch date. It has already missed an earlier deadline of April 1 for GST roll-out.
The bills being debated today are the Central GST bill, the Integrated GST bill, the Union Territories GST bill and the compensation law. Once these get Parliament's nod, a state GST bill will be presented in state assemblies for their approval.
GST is expected to boost the rate of economic growth by about 0.5 percentage points, broaden the revenue base and cut compliance cost for firms.
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