Various league officials had said during the past week that the NFL was going to crack down on violent hits to the head. Goodell made it official Wednesday by sending a memo and a video message to all the teams.
The commissioner instructed the head coach of each team to show the video and read the message to his players and coaching staff.
"One of our most important priorities is protecting our players from needless injury," Goodell said. "In recent years, we have emphasized minimizing contact to the head and neck, especially where a defenseless player is involved.
"It is clear to me that further action is required to emphasize the importance of teaching safe and controlled techniques, and of playing within the rules. It is incumbent on all of us to support the rules we have in place to protect players."
He said that even first-time offenders would be suspended.
The emphasis on violent hits came after a series of players were injured last weekend.
Cleveland wide receivers Josh Cribbs and Mohamed Massaquoi suffered concussions after hits by Pittsburgh linebacker James Harrison. Atlanta cornerback Dunta Robinson and Philadelphia receiver DeSean Jackson were both left with a concussion after they collided helmet-to-helmet.
Detroit linebacker Zack Follett, Washington tight end Chris Cooley and Baltimore tight end Todd Heap all suffered similar injuries after collisions.