United are not happy their local rivals have not offered the full 3,000 allocation at one end of the Etihad stadium on Arpil 7.
The Daily Mail claim the United top brass have made a complaint in writing to City chiefs to as the row escalates a month before the game.
Etihad sources has revealed they have been advised on safety grounds to limit the away end to 2,800, the same number recommended for the Champions League tie against Feyenoord last November.
United, whose numbers have previously been cut because of persistent standing, say behaviour has improved significantly in recent years.
The Premier League are aware of the row and could be dragged in to resolve the issue, although there is an acceptance that United's allocation is unlikely to change.
City have until later on Saturday afternoon confirm the allocation.
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Pep Guardiola could clinch his first league title that day and the problem between the two clubs comes after United denied a City film crew access to the Old Trafford tunnel earlier in the season.
Meanwhile, Guardiola has been fined £20,000 and warned of his future conduct by the FA for wearing a yellow ribbon in support of jailed politicians in Catalonia.
Guardiola maintains is not a political message, but will wear the ribbon before and after matches but not on the touchline.
City go to the bet365 stadoum on Monday night to face strugglers Stoke.
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