- Bopaiah, not the most senior MLA, made Speaker before trust vote
- Had disqualified 11 MLAs who had revolted against Yeddyurappa in 2010
- Move helped Yeddyurappa win trust vote, later cancelled by Supreme Court
Mr Bopaiah, 62, a five-time lawmaker, is a former speaker of the Karnataka assembly.
The Congress said his appointment is against the rules as he is not the most senior lawmaker in the assembly. Congress's RV Deshpande, an eight-time lawmaker, is far senior to Mr Bopaiah, said the party's Abhishek Manu Singhvi.
Describing him as "dented, tainted," the Congress also alleged that Mr Bopaiah had broken rules in the past to help Mr Yeddyurappa.
He famously disqualified 11 BJP lawmakers when they revolted in 2010 after Mr Yeddyurappa was charged in a mining scam. His move helped the BJP government of Yeddyurappa survive a trust vote but the decision was cancelled by the Supreme Court, which said he had not been fair.
"We are constrained to hold that proceedings conducted by the Speaker on Disqualification Application filed by B.S. Yeddyurappa do not meet the twin tests of natural justice and fair play," said the court, according to the Congress.
Mr Bopaiah was also pro-tem speaker in 2008, when the Yeddyurappa government fell short of a majority and had to depend on five independents to scrape through the trust vote.
Defending his appointment, BJP leader and union minister Prakash Javadekar said the Congress's objection was a "hoax" as even 10 years ago, Mr Bopaiah had been appointed pro-tem Speaker.
In a test of strength, the pro-tem speaker has to vote when there is a tie in the house.