Colin Kaepernick has filed a grievance against the National Football League, accusing owners of colluding to keep him from playing, according to reports from 6 ABC and Bleacher Report.

Kaepernick received national attention last year when he knelt at a football game during the national anthem. Then a San Francisco 49ers quarterback, Kaepernick explained that his act was a form of silent protest to raise awareness about police brutality and racial injustices in the United States. Critics of the quarterback have claimed that the act of “taking a knee” is disrespectful to the American flag and the military.

At the end of last season, the quarterback opted out of his contract with the 49ers and entered free agency, allowing him to play with other teams. But Kaepernick has yet to sign with a new team. His grievance accuses team owners of violating the league’s collective bargaining agreement.

Kaepernick’s lawyer, Mark Geragos, released a statement on Sunday.

“If the NFL ... is to remain a meritocracy, then principled and peaceful protest — which the owners themselves made great theater imitating weeks ago — should not be punished and athletes should not be denied employment based on partisan political provocation by the Executive Branch of our government,” Geragos said.