Manchester United have complained to the Football Association about their allocation of tickets for January's FA Cup third round tie at Manchester City.
Under FA rules, United are entitled to 15% of the capacity of the 47,805-seat Etihad Stadium, which is 7,100 tickets.
However, City have offered 5,500, just over 11%, on the grounds of safety.
United have special dispensation from the FA, due to Old Trafford's 76,000 capacity, to offer just over 11% to visiting fans, which is 8,500 tickets.
The Red Devils are demanding their full entitlement for the tie, which will kick off at 1300 GMT on Sunday, 8 January.
City, who are currently top of the Premier League, host their local rivals United, who are second, in the FA Cup for the first time since 1955.
The teams met in the semi-final of last year's competition with City triumphing 1-0 at Wembley before going on to beat Stoke by the same scoreline in the final to win their first major trophy for 35 years.
City thrashed United in their last meeting - a 6-1 Premier League victory at Old Trafford.