In a communication, the EC referred to the opinion poll broadcast by a TV channel on April 14 and said it included results of 111 Lok Sabha constituencies where balloting has taken place which "in effect becomes dissemination of result of exit polls in respect of the said constituencies."
The Commission did not name any channel, but the opinion poll was broadcast by NDTV.
This, the EC, said was violation of Section 126A of Representation of the People Act that prohibits publication and dissemination of exit polls.
"The prohibited period for this purpose is explained as 'the period may commence from the beginning of the hours fixed for poll on the first day of poll and continues till half an hour after closing of the polling in all the states and union territories'," it noted.
"...in order to maintain level playing field and to ensure free and fair elections, the Commission advises all print and electronic media not to resort to the type of practice as mentioned above, which for all practical purposes mean publication of exit poll while claiming that the same is only an opinion poll," the EC said in the communication addressed to all heads of all news organisations.
Earlier this month, the Election Commission had banned the publication and dissemination of exit polls of any kind from April 7, the first phase of Lok Sabha elections, till May 12 when the last phase of the polling ends.
The exit polls will be banned from 7 am on April 7 when polling in the first phase starts till 6.30 pm on May 12 when the polling in the ninth and last phase ends.
The Commission had also banned the publication of results of any opinion polls 48 hours before polling in respective areas.
Existing law allows EC to ban opinion polls 48 hours prior to voting.