Ferguson is already banned for 3 games for that offence, and now faces an additional 3 games if he is found guilty by the FA.
The FA stepped in after the referee on the night, Howard Dean, confirmed that he did not see the second incident, but that if he had, he would have sent Ferguson off again for it. It's rare for players to be sent off twice in one game, but it is possible, and the result would have been an automatic 6 game ban, which Ferguson is now almost certain to receive.