In a fresh letter to Internet and Mobile Association of India, it said as and when any "unlawful content" comes to the notice of websites, it should be removed "at the earliest".
It also asked the companies to ensure that the advertisers comply with the guidelines of the Commission regarding use of social media and internet platform for election campaign.
The poll panel said political parties and candidates placing advertisements on websites should be cautioned beforehand to comply with the various provisions of the Model Code of Conduct.
It had also also asked the internet sites to inform the Commission regarding the expenditure incurred by political parties and candidates on political advertisements as and when demanded.
The panel emphasised that no political advertisement should be accepted and displayed on internet and internet- based media without pre-certification.
It asked the internet-based media to carry out scrutiny to ensure that contents displayed by them during the electoral process is not unlawful, malicious or violative of the Model Code of Conduct which came into force on March 5.
