BJP MLA and Leader of Opposition Suvendu Adhikari said on Thursday, “The Speaker’s decision to claim Mukul Roy a BJP MLA was taken at the behest of the chief minister Mamata Banerjee. The move was a challenge to the Constitution.”

“Unfortunately, he was still called a BJP MLA though he had been attending Trinamool Congress meetings and other programmes. This is unprecedented and unheard of before,” Suvendu told reporters.

Roy was made Union railway minister for about six months in 2012 under former Prime Minister Manmohan Singh. He was also a Rajya Sabha member representing the Trinamool Congress.

The anti-defection law has been tested again and again since the Trinamool Congress came to power in 2011.

A member of the House belonging to any party shall be disqualified if he or she has (a) voluntarily given up membership of a political party or (b) votes or abstains from voting in such House contrary to any direction issued by the political party to which he belongs, according to the 10th Schedule of the Constitution.

The onus to decide on defections depends on the Speaker, with no time limit to make a decision, it states.

As many as 16 legislators remained on paper with the Congress though they were politically active with the Trinamool Congress in 1998 when it was formed in the state.