Rao, the parliamentary leader of the TRS, said party president K Chandrasekhar Rao has decided to support the combined opposition candidate Alva.
TRS MPs have been advised to vote accordingly, Rao said outside Parliament.
Alva will meet TRS MPs in the evening, he added.
In the presidential poll also, the TRS had sided with the opposition and supported Yashwant Sinha.
Alva has been fielded by the opposition against the ruling NDA’s nominee Jagdeep Dhankhar.
The vice-presidential poll will be held on Saturday.