Over one lakh activists and supporters of the nine-party alliance participated in the protest in the capital as a major strength show against Prime Minister Prachanda-led coalition government's move.
The protesting parties have been claiming that the bill was anti-constitutional and against national interests as it was brought out to serve interests of external forces.
The ruling alliance, mainly comprising CPN Maoist Centre and Nepali Congress, has been making efforts to amend the Constitution aiming to address the demands of agitating Madhesi parties.
Re-demarcation of the provincial boundary and citizenship issue are the two major demands put forth by the Madhesis.
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The Supreme Court in a recent verdict gave green signal to the government to amend the Constitution, rejecting a plea by the Opposition groups to stay the amendment Bill.
Besides CPN-UML, eight smaller left parties including CPN- ML and Nepal Workers and Peasants Party (NWPP) also joined the rally against the government.
Addressing the public meeting, Oli said the government should not push the Constitution amendment bill even after the Supreme Court's verdict and hoped that it would withdraw the bill before Sunday's House meeting.
"Anything which is against the Constitution will be invalid as per the Supreme Court ruling and the amendment bill registered by the government in the Parliament violated the constitutional provision," he said.
He said his party will not compromise on issues such as nationality, democracy, social justice, national unity and prosperity and cannot tolerate "humiliation of dignity".
Arguing that the proposal would not serve interests of Nepali people, he said people of the proposed Province No 5 has strongly protested the proposedmove to split the province.
He alleged that the Madhes-based parties are "working to destroy the native identity and languages of the region though they claim to promote the same."
Oli said the parties were trying to establish Hindi as an official language so as to belittle Maithili, Bhojpuri and Abadhi languages being spoken in the plains for centuries.
Speaking in the rally, CPN-ML General Secretary CP Mainali, Rastriya Janamorcha Chairman Chitra Bahadur KC, Nepal Workers and Peasants Party lawmaker Prem Suwal, criticised the government and ruling parties for registering the Constitution amendment bill, which they said is against the national interest.
Madhesis, mostly of Indian-origin, launched a six-month- long agitation from September 2015 to February last year in which more than 50 people were killed.
The agitation had also crippled the landlocked country's economy as supplies from India were blocked.