Treach says Tupac's rape accuser is only coming forward now to repeat her more than 2-decade-old allegations because she's trying to use the #MeToo movement to gain some fame.

The Naughty by Nature rapper tells us everyone heard Ayanna Jackson's story when Tupac went to trial and eventually prison in 1995. Treach, who was tight with 'Pac, believes Jackson is digging up the old story as part of what he calls, "the new hustle" -- promoting some upcoming project.

He clarified, he's not condoning rape, and clearly believes his friend did NOT commit one.   

As we reported ... Ayanna claims Pac told her he wanted to share her with his crew and forced her into group sex. Although she alleged rape, Pac was ultimately convicted of a lesser charge, first-degree sexual abuse.