West Ham say they are "surprised and disappointed" by UEFA's decision to ban supporters from attending their next Europa League away tie with Rapid Vienna.
The Hammers were charged following their 2-2 draw against Genk in Belgium on November 4. European football's governing body accused travelling supporters of crowd disturbances and the throwing of objects during their match in Belgium.
Those charges have been upheld and the club have been fined just under £25,500 (€30,000) for those disturbances and another £3,817 (€4,500) for the throwing of objects at the same game, and away supporters will not be able to attend the Rapid Vienna clash on November 25 despite some already buying tickets.
But West Ham say they are "urgently seeking clarification from UEFA, particularly given the extremely short notice of the sanction, which will impact our supporters who have already bought tickets and made arrangements to travel to Austria".
A statement continued: "We are surprised to receive these sanctions and disappointed for the fans who have behaved impeccably and supported the team throughout and will now be unable to travel to the next away Europa League fixture.
"The club has requested the full written reasons from UEFA regarding these sanctions and have asked them to expedite our request given that further delay could impact supporters once again.
"The club fully appreciates that supporters will have booked return travel and accommodation in Austria and are stressing this in our dialogue with UEFA. We will update supporters as soon as we are able to with further information.
"Finally, we would like to assure those supporters who have already purchased one of the 1,700 tickets that sold out our allocation for this game that they will be automatically refunded by the club should UEFA rule the sanctions stand and that they relate to next week's match in Austria."
UEFA's statement on the decision on Monday read: "The UEFA Control, Ethics and Disciplinary Body (CEDB) has announced today the following decision for the group stage match KRC Genk vs. West Ham United FC (2:2), played on November 4 in Belgium.
"Charges against West Ham United FC: Crowd disturbances, Art. 16(2)(h) of the UEFA Disciplinary Regulations (DR), throwing of objects, Art. 16(2)(b) DR. Decision: The CEDB has decided: to fine West Ham United FC €30,000 and ban the sale of tickets to its away supporters for the next one (1) UEFA competition match, for crowd disturbances, (and) to fine West Ham United FC €4,500 for throwing of objects."