Harrison is expected to miss Monday night's game against the San Francisco 49ers, though he has appealed the suspension, his agent told The Associated Press.
Harrison's agent Bill Parise said Tuesday afternoon that he expects the appeal to be heard later this week by Art Shell or Ted Cottrell, jointly appointed by the NFL and the players' association to hear such cases.
The odds of a successful appeal are small. Shell declined to reduce the two-game ban given to Detroit Lions nose tackle Ndamukong Suh after Suh stomped on an opponent's arm last month.
Harrison becomes the first player to be suspended for a helmet-to-helmet hit at a time when the NFL commissioner Roger Goodell has attempted to enforce enhanced player safety rules.
While he is suspended, Harrison cannot practice with the Steelers or be at the team's facility or a stadium where they will be playing. He is scheduled to be reinstated Dec. 20.