The Gunners' home ground can hold 60,338 fans, with 15% of the capacity allowed for visiting supporters, according to Football Association rules.
In this case, the North London outfit have allocated 5,168 tickets for Liverpool fans rather than the permitted figure of 9,050.
The Reds supporters' union Spirit of Shankly said in a statement: "In our letter to both clubs last week, we made clear that as well as reduced ticket prices and consideration being taken for the impact on supporters travel arrangements with regards to any proposed kickoff time, that we wished to be given the full 15% allocation in line with FA rule (21.(a)).
"This would amount to approximately 9,000 tickets, somewhat higher than the announced allocation. As a result, we have immediately re-written to both clubs today to ask them to explain this decision, given the absurdity that a football club can designate an area as being available to away supporters yet then raise fears over potential safety issues."
Arsenal announced last week that the game will be recorded as a Category B clash, which puts Liverpool's tickets in the lower price range as opposed to Category A, which could have one fan spending close to £100 for a seat.
The Spirit of Shankly later released a joint statement with the Tottenham Hotspur Supporters' Trust, Arsenal Supporters' Trust and Arsenal's Black Scarf movement expressing their "disappointment" at the situation.