Production sources tell TMZ ... the altercation went down Wednesday during filming of VH1's "Hip Hop Squares."
DeRay accused Tamar of lip-syncing, as a joke. She wasn't in earshot but noticed others laughing ... prompting her to ask what was so funny.
We're told Lil Mama relayed the joke to Tamar, and that's when she went off ... getting all up in DeRay's grill, but he wasn't having it. We're told DeRay barked back he didn't care who Tamar was or who her sisters were ... because he'd get HIS sisters to beat her ass.
For what it's worth ... Tamar was accused of lip-syncing her BET performance back in June.
They were eventually separated and filming resumed. No lingering beef, though. We're told Tamar and DeRay hashed things out after the show, which BTW returns Sept. 25 at 9/8c.
We reached out to DeRay and Tamar's camps ... so far no word back.