The BJP MLAs would not vote as the party did not support any of the contestants -- Prime Minister Manmohan Singh and Santius Kujur of the Congress and AIUDF's Aminul Islam, Sonowal told reporters here.
The BJP has five members in the 126-member House.
The Prime minister's victory is certain as he is the only contestant for the first preference votes of the 78 Congress legislators, while Kujur and Islam are tied for the second seat from the state, which has seven seats in the upper house.
Santius Kujur is an Adivasi leader from the Christian community who had contested the last assembly polls from Panery in Udalguri district, while Aminul Islam is AIUDF's general secretary and an advocate in the Gauhati High Court.