Independent MP Geoff Shaw has been involved in an altercation with taxi protesters on the front steps of the Victorian Parliament.
The ABC has seen video footage of the incident but it is unclear how it started. A man left the scene with a bleeding cheek.
Louie Karkatzoulis, who took the footage, described what he saw.
"I was just walking up. I took some video footage of Mr Shaw physically pushing a man down and swinging his arms around and causing physical damage towards their faces," he said.
Sergeant Chris Marsh says police are investigating the incident.
"We've got conflicting stories at the moment about some things that were said to us here, and some things from other witnesses," he said.
Mr Shaw, a former Liberal MP who turned independent earlier this year, holds the balance of power in the the Parliament.
The Member for Frankston is facing charges over the alleged misuse of his taxpayer-funded car and fuel card to help run his hardware business.
He would be required to vacate his seat if convicted, and a by-election loss for the Liberals could force an early general election.