In a statement, party leader Randeep Singh Surjewala said the BJP should provide an answer to people over defections from various parties and the process "is murder of the Constitution and democracy".
He said the BJP not only wants 'one nation, one election' but "one party" also and "its political conduct to engineer defections from opposition parties is denigrating the Constitution".
He said the BJP must realise that people have given it more responsibility to uphold constitutional norms and ethos.
"Its conduct has been simply the opposite. Latest instance is the illegal and unconstitutional manner in which it engineered defections among the Rajya Sabha MPs belonging to the TDP in an attempt to manufacture majority in Rajya Sabha. Congress questions the culture of defections systematically being cultivated by the BJP," he said.
The Congress leader said that defections "were based on threats, coercion, money power, muscle power and enticements".
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"Horse trading is now the bedrock of BJP's so-called expansion. This phenomenon, sans any ideological moorings, is murder of the constitution and democracy," he said.
Surjewala said Prime Minister Narendra Modi had claimed during electioneering in the Lok Sabha polls that 40 Trinamool Congress MLAs were in touch with him and this was "a brazen attempt at horse trading". He said legislators and councilors of Trinamool Congress have joined the BJP after the elections.
Referring to Arunachal Pradesh, he alleged that BJP "subverted all well-established democratic norms for power by hook or crook".
He said Presidents' rule was imposed in Uttarakhand to topple the democratically elected government but the Supreme Court quashed the decision in May 2016.
Surjewala said BJP has engineered defections in the Congress from time to time. Referring to Goa where Congress had emerged as the single-largest party in the last assembly elections, he said the "BJP committed a daylight robbery of the mandate by forming a government through the Governor".
"In October last year, two Congress MLAs joined the BJP. It later engineered a split in the Maharashtra Gomtantrak Party," he said.
Surjewala said that "Operation Kamala" was conceived in Karnataka by the BJP "to lure" opposition MLAs and alleged that one of its leaders "was caught in a tape".
Referring to Rajya Sabha elections in Gujarat last year, he said BJP had "lured" at least 14 Congress MLAs.
"Seventeen Congress MLAs have either resigned or joined BJP in the past two years and several have been made Ministers," he said.
Surjewala alleged that in November last year, BJP attempted to engineer a split in the Peoples Democratic Party as 18 of the party's MLAs "were supposed to break ranks and join Sajjad Lone-led People's Conference".
Referring to Maharashtra, he said Leader of Opposition Radhakrishna Vikhe Patil was lured by the BJP and has been made a minister in the Fadnavis government.
Surjewala said that in Telangana, 12 out of 18 Congress MLAs merged their party with "BJP's B-Team Telangana Rashtra Samithi recently". .