Fat Joe‘s former hype man says in a new lawsuit he saw the rapper have sex with underage girls who were 15 and 16 years old … but Joe says the allegations are BS.

Terrance “T.A.” Dixon filed a lawsuit Thursday claiming there were at least two minor females Fat Joe had sexual relations with, and another he allegedly fell in love with.

In the docs, obtained by TMZ, Dixon’s attorney, Tyrone A. Blackburn claims a 16-year-old Dominican girl would perform oral sex and other sex acts on Joe in exchange for cash, clothing and cell phone bill payments.

In the suit, Dixon claims Fat Joe was in love with a Latina he met when she was 15 years old. He says Joe paid all the girl’s bills, took her overseas for tours, put her up in a condo near where he lived with his wife in Florida and contemplated leaving his wife for her.

Dixon says Joe has an unhealthy and troubling fixation on underage individuals and raps about it in “She’s My Mama.”

Joe’s ex-hype man also says Fat Joe coerced him into having sex with women after concerts — sometimes in full view of other people — and says Joe underpaid him, denied him songwriting credits, and concealed royalties and backend payments.

Fat Joe’s attorney, Joe Tacopina, tells TMZ … the lawsuit is a blatant act of retaliation for a civil suit Joe filed against Dixon.

Tacopina says the allegations are “lies intended to damage his reputation and force a settlement through public pressure” … and he claims law enforcement is aware of what he says are extortionate demands from Dixon.

As we first reported … Joe sued Dixon back in April for defamation after Dixon allegedly made similar pedophile allegations against Joe on social media.