EXCLUSIVE

Melissa McCarthy's got some serious pull on the set of her new movie -- 'cause the "Bridesmaids" star just FIRED an extra for mistreating her own little kid on set ... TMZ has learned.

It happened yesterday in Wilmington, NC ... where she's filming "Tammy," directed by her hubby Ben Falcone.

The extra, a woman in her 20s, brought along her child -- age approximately 4-5 -- for the daylong shoot by a lake ... and the standard $58 payday ... sources tell TMZ.

Witnesses say the young mom had been struggling with her kid all morning ... constantly harping on the child to "stop it" and quiet down ... loudly enough to disrupt the production, which included more than 200 extras.

Sources say the last straw came when the mom harshly jerked the child up in the air by the wrist -- and McCarthy saw it all. The director IMMEDIATELY had PAs bounce the woman ... saying she wouldn't tolerate abuse on her set ... and that was that.

The woman's identity was not disclosed. Reps for McCarthy had no immediate comment.