The Bharatiya Janata Party hit back, saying Trinamool's attack on Modi was indicative of its "political bankruptcy".
Trinamool's national general secretary Mukul Roy said Modi's charge against their chairperson was a "blatant lie" and shot off a letter to the Election Commission.
"Yesterday (Sunday), he claimed that one of Banerjee's paintings was sold for Rs.1.8 crore. Either he should prove it or take his words back ... we seek an unconditional apology," Roy said.
He said it was a violation of the model code of conduct, and was "tantamount to character assassination".
"We strongly oppose it," Roy told reporters here.
Addressing a party rally in Sreerampore in Hooghly district Sunday, Modi attacked the state government over the Saradha chit fund scam and raised questions about Banerjee's painting being sold at an exorbitant price.