West Ham United supporters have been banned from travelling to the Europa League game at Rapid Vienna as a result of incidents in their draw with Genk.
Uefa charged the Hammers with crowd disturbances and for their fans throwing items on Cegeka Arena’s pitch.
The Hammers say they are “surprised” by the sanction are “disappointed for the fans.”
West Ham, who can appeal and ask for the ban be suspended until it is heard, are “urgently seeking clarification”.
However, if their appeal was to fail it would mean no Hammers fans would be able to attend their first away game in the Europa League’s knockout stage.
The London club have also been fined a total of 34,500 euros (£30,000).
West Ham said supporters are being punished with “extremely short notice” and added that their allocation of 1,700 tickets for the match on 25 November had already sold out.
The Premier League side has requested that European football’s governing body provide “full written reasons” for the sanctions and “have asked them to expedite our request given that further delay could impact supporters once again”.
“We are surprised to receive these sanctions and disappointed for the fans who have behaved impeccably and supported the team throughout,” the club said in a statement.
“The club fully appreciates that supporters will have booked return travel and accommodation in Austria and are stressing this in our dialogue with Uefa.”
West Ham are top of Group H with 10 points after four games.
The draw against Genk in Belgium on 4 November was Hammers boss David Moyes’ 1,000th match as a manager.
