"It is an election campaign. What is the EC doing?" he asked in a tweet, reacting to PM Modi displaying his vote finger while moving about on an Ahmedabad road after casting his vote.
In other tweets, Mr Chidambaram said the images on TV would leave no one in doubt that the Bharatiya Janata Party (BJP) and PM Modi conducted a full-fledged campaign on polling day.
"Shocking violation of rules. EC is sleeping on the job," he said.
The former Union Minister urged the media to look at the images on TV screens and search its conscience. "There has not been a more blatant violation of the code of conduct on polling day."
He added: "Stand up Media to this unprecedented violation of the code of conduct. Condemn the EC for allowing this gross abuse."
Mr Chidambaram also said that the BJP petitioning the Election Commission against the Congress was an act of desperation.
An interview after the campaign ends was the norm for every candidate and every campaigner in every election, he said.
"Yesterday, PM gave a speech. BJP's President gave an interview. Railway Minister gave an interview. Why have all these escaped the EC's attention? Why pick on only Rahul Gandhi's interview," he said.