Polling is underway to determine whether Indian National Congress will have former opposition leader, Mallikarjun Kharge, or former federal minister Shashi Tharoor as its next party president.
The voting, which began at 10.00am (IST), (4.30 GMT) will continue until 4.00pm. The results are expected to be announced on Wednesday, 19 October.
Almost 9,000 Pradesh Congress Committee (PCC) members will vote in different states of India.
Many senior members of Congress have already expressed their support for Kharge, who is also being called "Congress' unofficial official candidate! by many media outlets.
If elected, 80-year-old Kharge, who also comes from the Dalit community, is likely to play an important role in the citizens' minds, especially in his home state Karnataka. The move also comes after the federally ruling Bharatiya Janata Party (BJP) made Draupadi Murmu, who comes from the tribal community, the country's president.
State assembly elections in Karnataka are due to be held next year.
Tharoor recently accused Congress party delegates of being biased.
The 66-year-old senior parliamentarian said that Congress regional leaders have been "unavailable" whenever he visited any state, whereas his rival Kharge allegedly received preferential treatment.
According to the Hindu newspaper, Kharge held meetings with 25 Congress state units, whereas Tharoor held meetings with seven state units.
Congress is a center to center-left nationalist party which was founded in 1885 by British civil servant, Allan Octavian Hume. Traditionally, the party chief has been elected unanimously. The first election of the Congress party was held in 1939, when Netaji Subhas Chandra Bose won.