"Our party will support the JDU candidate in the Rajya Sabha's deputy chairman election," Mr Patnaik said on Wednesday, attributing the decision to his party's conviction that there should be unanimity in appointment to constitutional posts.

Mr Patnaik said PM Modi, Amit Shah and Nitish Kumar had also phoned him to seek support of his party's nine lawmakers. The BJD had skipped voting in last month's no-trust vote against the government in the Lok Sabha, reportedly at the BJP's request.

The BJP's estranged ally, the Shiv Sena has decided to go along with the NDA candidate this time. Senior Sena leader Sanjay Raut, who is frequently seen attacking the BJP, will move one of the four motions proposing Harivansh Narayan Singh's name. The Sena has said it was supporting the NDA candidate as this is an "apolitical" post.

The majority mark in the 244-member Rajya Sabha is 123. But some parties could abstain, pulling down the majority mark.

The Mehbooba Mufti-led Peoples Democratic Party says its 2 members will stay away from the election. Arvind Kejriwal's Aam Aadmi Party has also threatened to do the same unless Congress president Rahul Gandhi calls up Chief Minister Kejriwal to seek support of its three members. If both stay away, the majority mark could drop to 120.

BJP floor managers say the NDA candidate would, apart from the NDA's 91 votes, get support from AIADMK's 13 members, Telangana Rashtra Samithi's 6 members, four nominated and independent members.The NDA is also expecting support from the YSR Congress's 2 members.

"We have numbers on our side and Harivanshji will comfortably win the election tomorrow. It would have been better if the deputy chairman was elected unanimously," Minister of State for Parliamentary Affairs Vijay Goel said.

The opposition camp is seen to have the support of various parties, including Congress, Trinamool Congress, DMK, Left parties, Samajwadi Party, Bahujan Samaj Party and Nationalist Congress Party.

An addition to the opposition camp is Chief Minister N Chandrababu Naidu's Telugu Desam Party, which exited the NDA earlier this year but had been perceived to have been cagey about being seen to be working too closely with the Congress.