Prime Minister Narendra Modi is inaugurating India's new parliament building amid a boycott of the ceremony by 20 opposition parties.
The opposition has criticised the government for not asking the president to open the new building.
They also denounced the decision to hold the event on the birth anniversary of Hindutva ideologue VD Savarkar.
The ruling Bharatiya Janata Party (BJP) has called the boycott a "disrespect of democracy".
The new parliament building is part of the government's ambitious project to develop the Central Vista power corridor in capital Delhi.
On Sunday, Mr Modi will also unveil a new 75-rupee coin to commemorate the event and serve as a tribute to 75 years of India's independence.
Built in front of the colonial-era parliament, the new four-storey building - built at an estimated cost of 9.7bn rupees ($117.1m, £94.2m) - has increased seating capacity.
The Lok Sabha chamber, which will seat the lower house of the parliament, is designed in the likeness of a peacock, India's national bird. The Rajya Sabha chamber, which will seat the lower house, is designed resemble the lotus, India's national flower.
Last week, 20 parties - including the main opposition Congress - had announced their "collective decision" to boycott the inauguration ceremony.
Congress president Mallikarjun Kharge and party leader Rahul Gandhi said that the building should have been inaugurated by President Draupadi Murmu, the parliament's highest constitutional authority.
Congress MP Jairam Ramesh also criticised the government's decision to hold the event "on the birth anniversary of the man [Savarkar] who opposed Mahatma Gandhi vehemently all his life".
Commentators say the row reflects a fractious milieu where the ruling party and the opposition are unable to reach an agreement on most issues.
"Both sides need to find a way out of the separate corners they have backed themselves into. They must do so because history will not forgive them if they won't," The Indian Express newspaper argued in an editorial. "They must do so, for the sake of the people, and for the people's parliament."
As the new parliament is inaugurated, it will also witness protests by India's top wrestlers outside the building.
The wrestlers, including Olympic medallists, have been on a months-long protest at Jantar Mantar, a heritage site in the capital Delhi, demanding the resignation and arrest of their wrestling federation president, Brij Bhushan Singh
Singh, an influential lawmaker and politician from BJP, is accused of sexual abuse and harassment of female wrestlers - allegations he denies.
Source: BBC
BDST: 1150 HRS, MAY 28, 2023
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