'Love & Hip Hop: Atlanta' Star -- My Sister Attacked Castmate ... But I Didn't Order a Hit

"Love and Hip Hop: Atlanta" star Bambi Johnson adamantly denies putting a hit out on castmate Erica Pinkett -- but says she is related to the attacker.

Bambi says the woman -- Stephanie Harp -- who's accused of slicing Pinkett with a razor blade during a nightclub brawl earlier this month is her sister ... Johnson says Erica started the fight.

Bambi claims her sister says Erica threw a drink first -- triggering the fight inside Atlanta's Taboo nightclub. Bambi also claims her sister did not have a razor blade ... adding reports claiming the scene was bloody are false.

As we previously posted ... Erica says Bambi ordered the attack because the two have had arguments over Johnson's boyfriend Lil Scrappy.