Furthermore, Mackie was hit with a £1500 fine, a further £1500 fine will have to be paid in August 2004.
Mackie pleaded guilty to using threatening behaviour and/or insulting words to Sheffield United forward Carl Asaba following the Blades 2-0 victory over Reading at the Madejski Stadium in December.
"He will serve a 3-match ban starting on 17th March with another 5-match ban suspended until the end of the 2003-04 season," said an FA spokesman, speaking to TheFA.com.
"In the event of a similar incident before that date, this additional suspension would be activated with immediate effect."
It had been alleged that Mackie aimed a punch at Asaba in the tunnel as the players trapsed off following December's encounter
It has also been reported that the incident continued when the players came back out onto the pitch to warm down, with the pair reportedly having to be separated by a steward.
Whilst Mackie was unavailable for comment today, speaking in the immediate aftermath of the incident back in December, Mackie said: "I made the comment when I was still pumped up after the game, during which I had a tussle with Carl.
"I deeply regret making the comments and I know that I have let myself and Reading Football Club down."
Meanwhile, it has been confirmed that Reading captain Aide Williams will miss the home game against Wolves on Wednesday 12th March as he must serve a one-match ban for picking up five bookings this season.