"Thank you Sonia Gandhiji for your invitation to Iftar on Monday. My good wishes. As I am in Kolkata, Derek O'Brien will be in Delhi on our behalf," Banerjee said in a statement.
Gandhi's invite to Banerjee to the Iftaar came just a week before the monsoon session of parliament.
A section of state Congress leaders want an alliance with CPI(M) to take on Banerjee-led Trinmoool Congress in next year's Assembly poll.