The contest is expected to be very tight in Rajasthan and Karnataka amid reports of differences within the Bharatiya Janata Party (BJP) over the candidatures of senior criminal lawyer Ram Jethmalani and liquor baron Vijay Mallya.
The BJP has fielded Jethmalani from Rajasthan, while Mallya is contesting as an independent candidate from Karnataka. The BJP is divided on whether to support Mallya, who is bidding for a second term as an independent supported by 27-member JD-S legislature group.
There are also five Rajya Sabha seats in Bihar, four in Karnataka, three in Orissa and two in Jharkhand to which elections are being held.
The other prominent candidates, whose fate will be decided today are Union Commerce and Industry Minister Anand Sharma, Lok Janashakti Party (LJP) supremo Ram Vilas Paswan, senior Congress leader Oscar Fernandes and former BJP President M Venkaiah Naidu.