Harlequins have launched an investigation into how thousands of Munster fans managed to buy tickets for their Heineken Cup quarter-final.
Munster won the game in front of a record crowd for the Stoop - 15,000 - and Harlequins are blaming their own fans for selling tickets on to opposition supporters on the web.
Munster sold out their allocation of 3,750 but many more than that obtained tickets for the match.
No tickets were available on general sale, with season-ticket holders, officials, organisers, sponsors and charities the only others with access to tickets.
In a statement on the club's website, Quins said: "Last Sunday it was obvious from 90 minutes before kick-off that Munster's well organised and wonderful supporters had a presence in the stadium that exceeded the number of tickets officially allocated to them.
"The colourful and vocal support they gave their talented team during the match provided further evidence of this if it was needed.
"Given the controlled manner that tickets were made available for the match, it is clear to the club that many of its "supporters" sold their tickets on to opposition fans.
"To say that this is disappointing for the players, coaches, management and staff of the club is an understatement.
"The club is determined to identify any person that sold on his or her ticket and will ensure that last Sunday's outcome is not repeated."