Harlequins have launched an investigation after claiming "many" of their supporters sold tickets on to rival Munster fans for last Sunday's Heineken Cup quarter-final at the Twickenham Stoop.
Under Heineken Cup participation rules, twice European champions Munster were allocated 25 per cent of available tickets (3,750) for the game, which attracted a ground record 15,000 crowd.
But in a strongly-worded statement published on the club's website, Quins said it was "obvious from 90 minutes before kick-off" that Munster supporter numbers "exceeded" their ticket allocation. Munster fans roared their team to an 18-12 success, setting up a semi-final appointment with French challengers Clermont Auvergne in Montpellier later this month.
"In the two weeks leading up to the match, the club was aware that tickets were being sold on Ebay and through other unauthorised channels," Quins said. "Where possible, it tried to identify the source of the tickets, the tickets involved and cancel them.
"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."