Michael Doyle, the Blades captain, was sent off 15 minutes into the game at Glanford Park for a stamp aimed the Iron's Mike Grella.
Ryan Flynn was also sent to the stands in the second-half, after a high tackle on full-back Christian Ribeiro.
At a hearing on Tuesday afternoon the FA ruled that referee Steven Rushton's original decisions should stand.
"We thought we had a good case so are very frustrated with the decision," said the Blades manager Danny Wilson.
The pair will both serve three-game suspensions, ruling them out of matches against Bury, Yeovil and Doncaster Rovers.
Source: FOOTYMAD
