Oakley is keeping Pitbull in the dark, and he ain't happy about it -- he says the sunglasses giant is slapping his name on a line of shades without his approval, so now he's suing.

In the suit, the rapper says Oakley is hawking Pit Bull (note it's 2 words) branded eyewear -- which is a major problem for him ... since Pitbull sells his own line of shades, including his Pitbull Dale Sunglasses.

Pitbull says Oakley sponsored one of his tours in 2009, and he wore their sunglasses at the time -- which he says proves the company knows there's good money in targeting his fans. So, he thinks it's no coincidence Oakley is continuing to use his name six years later.

He also blasts Oakley for jacking his "Pitbull" trademark with its "Pit Bull" line.

Pitbull wants Oakley to stop selling the shades, and he wants the profits made off those shades.

Or as he would put it ... "Dale!"