Blackburn have warned their supporters against selling season tickets to Manchester United fans for the crunch fixture between the two sides this weekend.
United will secure their 19th league title if they avoid defeat at Ewood Park on Saturday, while Rovers are looking for a positive result as they continue their battle to avoid relegation.
The sale of tickets to United fans could mean some supporters are not segregated, causing a security concern.
A statement on Blackburn's official website said: "Reports that some Blackburn Rovers supporters are 'selling' their season tickets to Manchester United fans ahead of Saturday's Barclays Premier League fixture at Ewood Park have brought a furious response from the club."
The statement continued: "Club officials - fully supported by Lancashire Police - warn that everything possible is being done to minimise the illegal practice and stress that any offenders will face strong and appropriate action.
"Rovers have information and intelligence of season ticket holders selling their tickets directly to United followers - there is even evidence of season tickets being advertised on the internet."
Blackburn managing director Tom Finn said: "This is a very disturbing situation, not to mention a criminal offence, and a situation we could well do without leading up to what is a massive fixture.
"We are currently monitoring things very closely and, where necessary, will cancel the season tickets, so denying entry to the stadium on the day.
"It also goes without saying that we need as many Rovers fans inside Ewood Park on Saturday as we can.
"Fervent home support has worked wonders for us in recent years and we need it again now."
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