Congress on 27th February won three of the four Rajya Sabha seats in Karnataka, while BJP bagged one.
All three Congress candidates Ajay Maken, Dr Syed Naseer Hussain and GC Chandrashekhar have been elected to the Upper House of the Parliament.
From BJP, Narayana Bandage won a Rajya Sabha seat. BJP-JD(S) joint candidate Kupendra Reddy lost the elections.
In a setback to BJP, MLA ST Somashekar cross-voted for Congress' Ajay Maken, while another saffron party legislator Arbail Shivaram Hebbar abstained from voting.
Somashekar represents Yashwantpur assembly constituency and Hebbar from Yellapur segment.
"We have got the information that Somashekar has done cross-voting. I believe that people do not like cheating every now and then," the Leader of Opposition R Ashoka told reporters here.
"I consulted with advocate Vivek Reddy who is our state legal cell president and a high court lawyer. We will ask the Speaker to initiate action against him (Somashekar) and explore the possibilities to take steps in accordance with the law," the former deputy chief minister said.
Somashekar had quit the Congress and joined the BJP. He served as the minister (in the BJP government) and was made the Mysuru district in charge.
Ashoka termed Somashekar's decision as "political suicide".
(With PTI inputs)