'Honey Boo Boo' Star Mama June -- My Daughter Is A Cyberbully ... And It's Stopping NOW

Mama June took a can of whoop ass on her daughter after she found out she was cyberbullying two girls in her class ... TMZ has learned.

13-year-old Pumpkin posted 2 cruel Instagram videos last week, ripping into 2 classmates ... calling them fat, ugly and annoying.

What makes it even worse ... 4,000 followers watched Pumpkin rail on the little girls.

The mother of one of the girls got wind of it and blasted Mama June on Facebook, calling her a hypocrite because June has been so active in anti-bullying campaigns.

When June realized what was happening, she went ballistic, and took swift action. For starters, Pumpkin had her Internet privileges yanked. June also ordered her daughter to apologize to all involved.

June tells TMZ ... "My family takes bullying very seriously. I do not tolerate it. As a mom, I jumped in, reached out to the parent and took action."

Pumpkin got the message -- she went back on Instagram, but this time to post an apology.