The officer, Parag Jadhav, was on duty outside a hotel room where Uddhav was having a meeting with some of his party legislators.
Harshavardhan tried to enter the room but he was stopped by Parag. Enraged over this, the MLA allegedly slapped the officer, police said, quoting from a complaint filed by the victim.
An offence was registered against the lawmaker with Sonegaon Police Station under whose jurisdiction the hotel falls, they said.
Maharashtra legislators have assembled in Nagpur, the state's second capital, for the ongoing winter session of legislature.