The Football Association have been called in to resolve a row between Manchester United and Manchester City over ticket allocation for the FA Cup tie next month.
The bitter rivals go head to head at the Etihad Stadium in over a fortnight, but the Red Devils have issued a complaint to the English governing body over the lack of tickets made available to United's supporters.
The Premier League champions have been allocated 5,500 tickets, but under FA rules the North West club are entitled to up to 7,100 seats.
While United are refusing to stand down on their demand, the blue half of Manchester are believed to be standing firm on the original number of away tickets offered.
