Sir Alex Ferguson has written to Manchester United's supporters to urge them to improve their behaviour at away matches or risk their ticket allocations being slashed.

Ferguson has become personally involved after United learned that their usual 3,000 allocation for the game at Liverpool on 15 October has been reduced to 1,960 because of problems involving their supporters at recent matches.

Twelve Premier League clubs refused to give United their full allocation last season and the champions are concerned it is becoming a trend that is costing innocent supporters the chance to follow the club while also putting the team at a disadvantage. A letter from Ferguson has been sent to all the United fans who have tickets for Anfield to express his concerns. Ferguson urges supporters to "respect the stewards and follow ground regulations" and says the alternative is that the club will continue to miss out on tickets for away fixtures.

"Despite intense lobbying by the club on your behalf, there will only be just over 1,900 United fans at Anfield," he says. "We can't allow this situation to continue. I've said many times that your support is a vital part of our success and, trust me, the players do notice when your numbers are cut."

One of the key issues is the persistent blocking of aisles and gangways by supporters standing during matches, making a potential obstruction for emergency services, but the club admit they have received other complaints. United officials raised the issue at the last meeting of the club's official fans' forum, explaining that "one of the reasons provided by clubs for giving a reduced allocation was safety, but the main reason was supporters' behaviour".

Tottenham Hotspur, Manchester City, Bolton Wanderers and Sunderland are among the Premier League clubs who have punished United, whereas Leeds United did the same as a precautionary measure ahead of their Carling Cup tie at Elland Road last month.

The clubs are acting on the advice of safety advisory groups, independent bodies whose representatives mainly originate from the local council and police. However, United have noted that Everton, using the same authority as Liverpool, have not penalised them and the Old Trafford club have been disappointed to learn that Liverpool have subsequently sold the tickets that have been withdrawn to home fans.

A delegation led by United's chief operating officer, Michael Bolingbroke, and the club secretary, John Alexander, has been to Anfield to discuss the issue and determine how in future seasons they can get a full allocation once again. There is an already a problem at United of too many fans for not enough tickets, with 164,000 applications for the 55,000 away tickets they were allocated in the league last season.

The club are also discussing the matter with the Premier League to get some clarity on the rules and establish whether clubs who remove tickets should be allowed to sell them to their own fans.

Wigan Athletic routinely allow United unusually large ticket allocations but withdrew some before last season's game at the DW Stadium, and United's information is that they were then sold as part of corporate packages. United's argument isthat it is unfair on them to be responsible for fans who have not bought tickets via the club and that the home club should not be allowed to make a profit out of it.