4:56 PM PT -- Colin's lawyer, Mark Geragos, released a statement saying ... "We can confirm that this morning we filed a grievance under the CBA on behalf of Colin Kaepernick. This was done only after pursuing ever possible avenue with all NFL teams and their executives." The statement goes on to say Colin shouldn't be punished for his peaceful protest, and that he just wants to get back to playing.

Colin Kaepernick has filed a grievance against the NFL alleging the league colluded to keep him out because of his National Anthem protests ... according to a new court filing.

The filing, obtained by ABC News, alleges the league's owners "colluded to deprive Mr. Kaepernick of employment rights in retaliation for Mr. Kaepernick's leadership and advocacy for equality and social justice."

Kaepernick has also hired celeb attorney Mark Geragos for representation as opposed to going through the NFL Players Association.

As we reported ... Kaep's protest has ignited a national debate about kneeling for the flag.