Police are investigating a pretty horrifying clip of cops pummeling a woman ... and we're told it all started after a complaint about lack of cheese on a Big Mac.
In the vid, you can see 2 officers attempting to detain Latinka Hancock Monday in Butler Township, Ohio. After some arguing, you can see one of the cops punch her in the head multiple times before getting the cuffs on her.
Police now say they're looking into the incident caught on camera.
Hancock's attorney Michael Wright of Wright & Schulte tells TMZ ... it all went down after Hancock ordered and paid for a Big Mac at McDonald's with extra cheese -- but she claims the order didn't come with the extra cheese.
Wright says employees ended up calling the cops on Hancock after things got heated ... and insists she was confronted by Butler Township PD after trying to leave.