Fat Joe's sneaker biz partner screwed over their customers -- even went to prison for it -- but now the guy's claiming Joe screwed him out of a ton of cash ... TMZ has learned.

Scott Spina is suing the Bronx rapper over a shoe store, UP NYC, which they opened together in November 2016. In the suit, Spina says he sunk a bunch of his own dough -- $150k -- plus he wrangled more than $300k more from investors and loans.

Spina claims it was all good when they opened their doors. According to the suit, obtained by TMZ, they hauled in $175k on their first day -- but he says 20 days later, Joe kicked him out of the biz.

The part Spina is leaving out is the fact ... he was eventually busted for stealing credit card info from his customers. Seems like Joe cut him off once he caught wind of Spina's sketchy dealings. Earlier this month, Spina was sentenced to 35 months in a federal prison.

Still, Spina says Joe owes him -- he's suing for his $150k personal investment, plus his fair share of UP NYC. We've reached out to Joe's camp, but no word back yet.

IF Spina wins, it'll mean big money ... for his prison commissary account.