Deputy Election Commissioner Sandeep Saxena told reporters that election authorities in Assam had told Gogoi that holding a press conference within 48 hours before end of poll was not advisable.
But Gogoi went ahead with the event where he reportedly alleged that a candidate and a former minister was detained in his house.
The Deputy EC said when the commission checked the facts, it was found that poll officials had gone to check whether there was a "congregation" at the candidate's residence and he was not detained.
Gogoi had also reportedly alleged that the EC was biased.
After checking the facts, the EC had directed the concerned district magistrate to lodge an FIR against the CM.
"The FIR has been lodged," Saxena said, adding that Section 126 of RP Act attracts penalty or 2-year jail or both.
The penalty has not been quantified in the law.
Under section 126 of the law, there is a prohibition of public meetings during period of 48 hours ending with hour fixed for conclusion of the poll.
It states that no person shall convene, hold, attend, join or address any public meeting or procession in connection with an election; or display to the public any election matter by means of cinematography, television or other similar apparatus; or propagate any election matter to the public by holding, or by arranging the holding of, any musical concert or any theatrical performance or any other entertainment or amusement with a view to attracting the members of the public thereto, in any polling area during the period of 48 hours ending with the hour fixed for the conclusion of the poll for any election in that polling area.
The Deputy EC said the Commission also verified reports that Assam's BJP leader Himanta Biswa Sarma took part in a "procession", which is against electoral laws. But EC found out that when he was returning from a temple, some people had gathered to have a "glimpse" of him and hence it was not a procession.
He, however, had reportedly made remarks of some financial irregularity and the Commission was looking into the matter.
High voter turnout in Assam, West Bengal polls
How the RSS plans to win Assam for the BJP
Stage set for final phase of polling in Assam
Modi alleging I did nothing for Assam not true: Manmohan
Opinion polls project hung assembly in Assam