While the allocation for the match should be around 9,000 tickets, Manchester United Supporters' Trust (MUST) said they have been told that Arsenal are offering only 5,000 tickets, citing "safety reasons".
"What makes the FA Cup special is the larger away allocations than you get in league games," a MUST spokesman said.
"For Arsenal to offer little over half the proper allocation is a joke. The game is just 10 days away and at present United are unable to sell tickets to their fans.
"Supporters need to make arrangements for a fixture which has already been shifted to an inconvenient Friday night kick-off time."
United supporters have been backed by their counterparts at Arsenal, who said they would expect a full allocation in case of a potential replay at Old Trafford.
"Set at 15 percent in rules. Creates great atmosphere and creates differentiation to PL (Premier League). So frustrating to see this under threat at Emirates for MUFC Cup tie," the Arsenal Supporters' Trust wrote on Twitter.
Despite the competition rules, Arsenal said the away allocations are set following discussions with their Safety Advisory Group.
"Ticket allocations are based on ongoing safety assessments and in consultation with our Safety Advisory Group, which includes representatives from the local authority and police," an Arsenal spokeswoman said.
Arsenal with 13 FA Cup wins and United with 12 are the most successful clubs in the world's oldest knockout competition.
(Reporting by Hardik Vyas and Alan Baldwin; Editing by Ian Chadband)
