The Opposition is stepping up the pressure on the government over Finance Minister Pranab Mukherjee's suspicion that his office was bugged. After Home Minister P Chidambaram told NDTV exclusively that he did not know about the bugging of Mr Mukherjee's office because it was a 'non-event', the BJP, today, demanded that Pranab Mukherjee's complaint letter to the Prime Minister be released.