The pair clashed during Manchester City’s 2-0 win at the KC Stadium last Saturday, with Hart believing Boyd had dived following his challenge in the box.
Replays appeared to show the Scotland international spitting towards the direction of the England goalkeeper, an action that has presented him with an FA misconduct charge.
The incident was missed by referee Lee Mason, meaning the FA have brought forward the charge having reviewed video evidence.
Boyd has previously been backed by his manager Steve Bruce following the incident.
“He [Boyd] has tried to talk and shout and something’s come out. That’s what I’ve seen of it,” Bruce said.
“George Boyd wouldn’t do that, no chance. Not deliberately, anyway. He is as honest as they come. He was playing non-league six years ago.”
Boyd also felt Joe Hart should have been shown a red card for his part in the incident, after he appeared to move his head towards Boyd as the pair clashed.
“He didn’t nut me but he’s put his head in, so he should have got sent off really,” Boyd said.
“He said afterwards that he didn’t touch me, but I thought he touched me a little bit. He apologised for the reaction and that’s it.”
Boyd is set to receive a three-match ban if he fails to prove his innocence, which could rule him out of the club’s upcoming Premier League games against West Brom, West Ham and Stoke.