50 Cent's 'Power' Stars Have Cold War Brewing Off Set

50 Cent's TV family is in full dysfunction -- 2 'Power' stars are on the verge of coming to blows, and the infighting is keeping everyone on their toes when cameras aren't rolling.

Sources close to the unfolding drama tell TMZ Hip Hop the problems between "Power Book IV: Force" actor Joseph Sikora and "Power Book II: Ghost" actor Gianni Paolo have been brewing long before Joseph -- who plays Tommy -- dropped a very public diss on Gianni.

50 and singer Joe were on stage in Houston last weekend performing the 'Power' theme song as several cast members joined them onstage.

When Gianni went to give Joseph a pound, he was brutally ignored ... and cameras caught the burn in real time! 😬

Gianni recently fired back at Joseph's claims of reconciliation following the onstage diss so yeah, Houston … there's still a problem!!!

Sources involved with the series back up Gianni's claims, noting there's been an air of coldness when the 2 actors are around each other.

We're also told the rivalry between 'Power II' star Michael Rainey Jr. and "BMF" actor Lil Meech is getting out of hand … with both camps aggressively throwing money at one another during a Houston Tycoon Fest party.

Their respective security teams almost came to blows as a result of the ruckus but we hear cooler heads prevailed to party on.

Last year, Meech and Mike revved up the testosterone on IG … sending shots to one another ahead of the "BMF" premiere and things are still, well … testy.

The last time we spoke to Gianni and Mike, they told us Fiddy was an incredible peer mediator on set … just from his presence alone.