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 brawl at Carrow Road, which saw Blades midfielder Stephen Quinn red carded, has also led to on-loan midfielder Andy Reid facing a charge of violent conduct following an apparent headbutt.
Reid, on loan from Sunderland, has until 6pm on Friday to answer the charge and if he accepts it, he will receive a standard three-match ban.
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.
Source: PA
Source: PA