NFLPA spokesman George Atallah said Thursday that the union has a responsibility to pursue all violations of the collective bargaining agreement consistently.
The Patriots are accused of holding Butler out of voluntary workouts because he was late for the first of the team activities. The Patriots and Butler have not publicly acknowledged the discipline, though Butler did tell reporters when he turned up at workouts that he had to deal with someone taking something away from him.
Butler became a Super Bowl hero last season when he intercepted Russell Wilson on the goal-line in the final minute. Since then, he's appeared on talk shows, got a parade in his hometown and even presented at the Grammys.