Arsenal have been sanctioned for refusing to provide Manchester United with their full allocation for the FA Cup third-round tie at the Emirates in January.
United were left frustrated after being given 8,000 tickets for the clash, 1,000 less than their entitlement under competition rules.
The Gunners had cited safety concerns as the reason for the decision, which United unsuccessfully challenged with the FA after making several complaints to the organisation in the lead-up to the match.
The seats in question were in an upper tier of Arsenal's 60,000-capacity Emirates Stadium and were left empty - despite United offering to handpick recipients, and ensure they went to families and children linked to the club's charity arm.
United then suggested they be handed to emergency service workers and those involved with FA grassroots projects, which was also rejected.
In a statement on Friday, the FA's Professional Game Board said Arsenal had been given a suspended £500,000 fine for failing to provide United with their full entitlement.
Arsenal refused to give Man United their full allocation and 1,000 seats were left empty
The Gunners have been hit with an FA sanction for failing to comply with FA Cup rules
'The fine is suspended pending Arsenal FC's confirmation that it is able to comply with this requirement for the 2025-26 FA Cup third round and continued compliance for any further rounds of this season's competition,' the statement read.
Arsenal's argument was United have been handed a 13 per cent allocation, with competition rules stating 'up to 15 per cent' should be offered.
The decision was taken by the Safety Advisory Group, which involves club officials, council officers and members of the emergency services.
Last season, Liverpool were given a similarly reduced allocation amid concerns over persistent standing in the upper tier.
United won the tie on penalties, Joshua Zirkzee scoring the deciding spot-kick following a fractious 1-1 draw after extra time.