When Tom Brady’s appeal hearing kicks off today, key arguments will be about who ordered his four-game suspension and whether science supports the league’s findings about deflated footballs.

The NFL says Commissioner Roger Goodell authorized the discipline that was imposed by league executive Troy Vincent, who signed the letters sent to Brady and the New England Patriots informing them of the penalties. The NFL Players Association challenged Vincent’s power to issue punishment, citing Article 46 of the league’s collective bargaining agreement.

“You have no authority to impose discipline on Mr. Brady under the CBA, and such discipline must therefore be set aside,” union attorney Tom DePaso wrote to Vincent on May 14. “The CBA grants the Commissioner — and only the Commissioner — the authority to impose conduct detrimental discipline on players.”

Goodell dismissed the union’s claim when he declined to recuse himself from hearing the appeal on June 23.

“I did not delegate my disciplinary authority to Mr. Vincent; I concurred in his recommendation and authorized him to communicate to Mr. Brady the discipline imposed under my authority as Commissioner,” Goodell said in his letter to the union on June 2. “The identity of the person who signed the disciplinary letter is irrelevant.”

Brady was suspended four games and the Patriots were fined $1 million and docked a pair of draft picks after investigator Ted Wells found that the Super Bowl champions illegally used under-inflated footballs in the AFC title game.

Vincent has issued several fines and penalties for various infractions since replacing Ray Anderson as the NFL’s executive vice president of football operations in March 2014.

He suspended former Redskins safety Brandon Meriweather two games last September for a helmet-to-helmet hit on a receiver. In several other cases, he fined teams or punished team officials for violating rules.

The NFLPA didn’t question Vincent’s authority in those incidents but it only gets involved when players are disciplined.