The Football Association charged the Blades with failing to control their players after two separate incidents over the Christmas period.
United were involved in mass confrontations in both of their festive fixtures, against Hull on Boxing Day and Norwich on December 28, and they face two separate charges.
The melee at Carrow Road, which saw Blades midfielder Stephen Quinn red-carded, also led to Reid facing a charge of violent conduct following an apparent headbutt.
Under the FA's fast-track regulations, the on-loan Sunderland man admitted the charge and accepted a standard three-match ban, which begins with the trip to Burnley on New Year's Day.
Hull and Norwich have also received charges for their part in the confrontations and all three clubs have until January 5 to respond to the FA.