Lil Wayne -- Young Money = No Money ... Lawsuit Over 'Mirror'

Lil Wayne is hoarding Young Money's money ... so claims a music producer who says Wayne & Co. screwed him out of tens of thousands of dollars.

Ramon Owen -- aka REO -- claims he produced Lil Wayne's song, "Mirror" for his 2011 album, "Tha Carter IV" ... which sold more than 2 million copies.

REO says in a new lawsuit Young $$$ promised him a cut of the profits. In fact, he says the company actually sent him a statement clearly showing he's entitled to $91K minimum. As for what he got ... zilch.

REO is suing Young Money and Cash Money ... for money.