50 Cent Lawsuit -- I LOST Because I'm Black

50 Cent says he got SCREWED in court recently because the judge was a rap-hating RACIST ... and now he wants the allegedly bias ruling overturned ... this according to court docs.

Earlier this year 50 and company called Sleek Audio were embroiled in a bitter lawsuit. 50 claimed Sleek owed him over $261,000. Sleek said otherwise. The case went to arbitration -- a binding process in which an arbitrator picks the winner.

Bad news for 50, the arbitrator sided with Sleek (the final $$$ judgement was kept under wraps).

But 50 refuses to go gently into that good night ... and is taking the battle to federal court -- claiming the arbitration judge discriminated against him because he's black, associates with controversial African-American figures AND because he's a high profile rap artist.

Specifically ... 50 says the bias ran so deep the judge didn't allow him to cross-examine witnesses and refused to look at evidence pertaining to the case. Pretty bold claims.

He wants the award axed ASAP and is asking for a new hearing ... where he says he'll prove the judge was out to get him from the get go.

Sleek fired back too ... claiming 50's allegations of racism are a desperate attempt to avoid the arbitration decision and get it brought before an actual court.