The non-NDA parties are set to meet on June 22 to discuss the issue.
According to the sources, former Lok Sabha speaker Meira Kumar, ex-Union Home Minister Sushilkumar Shinde; Bharipa Bahujan Mahasangh leader and grandson of Dr B R Ambedkar, Prakash Yashwant, and retired diplomat Gopal Krishna Gandhi are some of the names the opposition parties are considering.
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This, they said, was because the BJP is too close to winning the poll for the first time that it would not let go the opportunity.
"We will contest the polls. We feel there should be a joint opposition candidate. Since the BJP has named a Dalit, the opposition parties may finalise their consensus candidate on the same line," a sources said.
The BJP made the "unilateral" move probably to revive its image post the alleged attacks on Dalits in the recent past ahead of the next general elections polls and picked a candidate from the politically most crucial state, Uttar Pradesh, the sources observed.
They asserted that the opposition unity is very much there.
Before Kovind's name was announced, the opposition parties had also thought about fielding a tribal candidate, they said.
"There was word doing the rounds that the NDA would field Jharkhand Governor Draupadi Murmu, a tribal woman leader. So, we were also considering to field a tribal person. But now that they have named a Dalit leader, the equations are altogether different now," the source added.