After receiving a complaint, Fatehgarh Sahib SSP marked the inquiry to Bassi Pathana DSP with the directions to submit the report at the earliest.
Media persons told the SSP that Mann had arrived four hours late in yesterday's rally and was disappointed after finding a "thin gathering" awaiting him.
Mann instigated AAP volunteers against media persons present there who manhandled them and even damaged camera of one journalist, the complaint read.
Mann even used word "paid media" which hurt the feeling of journalists, it said.
Zila Patarkar Union, Fatehgarh Sahib President Ranbir Kumar Jajji threatened to launch an agitation if the case was not registered against Mann by September 3. He said he was even ready to sit on a hunger strike.
Meanwhile, Congress activists burnt an effigy of Mann at Bassi Pathana.
Targeting the print media, Mann had asked volunteers not to read newspapers, alleging influence of money in publication of news.
Mann felt enraged when media persons asked him why he was four hours late for the party's rally, it said.
He shot back and said, "We don't need any media reporting of AAP's functions," it added.