Fetty Wap sued...he cheated Benjamins for '679'

Fetty Wap ruthlessly cut the lyrics written by a former Remy Boyz member for his mega hit "679" and cheated him out of major cash ... so claims Fetty's ex-homie.

Rapper P-Dice says he helped write the multi-platinum song, and Fetty cut a deal to give him 16.9% of the profits off the track, but in a lawsuit PD says he was scrubbed from the song to avoid the payout.

According to the docs, Fetty verbally agreed to give P-Dice writing credit -- but after they finished recording, Fetty deleted his entire performance and reduced his share of the profits to 5%.

P-Dice -- who appears prominently in the "679" music video -- says the edited version ended up on Fetty's album which debuted No. 1 on Billboard. The music vid alone has topped 238 million views.

P-Dice is suing for damages in excess of $7 million. A rep for Fetty had no comment.