(ABC News) -- Former San Francisco 49ers quarterback Colin Kaepernick has filed a grievance against the NFL, alleging the owners colluded to keep him out of the league because of his protests during the playing of the national anthem before games.

The grievance 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."

The NFL did not immediately respond to a request for comment.