England manager Roy Hodgson has written to ticket holders for Wednesday's friendly against Ireland asking them to behave, in the first meeting between the teams since English supporters caused the abandonment of a match in Dublin in 1995.
The Dublin friendly 18 years ago was stopped after 27 minutes when England fans rioted by ripping out seats and throwing them towards the pitch. Their motive was hatred of the IRA, and the FA fears IRA chanting at this week's fixture at Wembley.
In the email, Hodgson writes: "Ahead of the Ireland fixture, on behalf of the FA, I would like to ask our supporters to please respect our opponents and welcome them in the right way.
"Wembley is considered the world over as the home of football and we ask those attending not to take part in any chanting - particularly of a religious or political perspective - which could cause offence to our visitors or fellow fans.
Manchester City and Chelsea fans have packed out Wembley Stadium this afternoon as their teams clash for a place in the FA Cup final.
Police said they are investigating incidents involving Millwall supporters at today's FA Cup semi-final that left some fans bloodied and younger ones in tears.
A Scotland Yard spokesman said:
Millwall football fans fought each other at Wembley as their side lost 2-0 to Wigan in the FA Cup semi-final today.
Police intervened after MIllwall fans fought each other in the stands at Wembley as the London club lost 2-0 to Wigan Athletic in the FA Cup semi-final.
Former Millwall player Paul Ifill said Lions fans who fought each other in the stands during today's FA Cup defeat to Wigan "tainted the day".
Wigan Athletic have reached the FA Cup final for the first time in their history, beating Millwall in a match that was marred by scenes of violence involving fans of the London club.
Shaun Maloney and Callum McManaman scored in a 2-0 win for the Latics, whose victory means the club qualify for Europe.
Millwall fans could be seen fighting each other in the stands throughout the second half of the Wembley semi-final.
The winning crew finished in 17 minutes and 27 seconds to cut Cambridge's overall lead to 81-77.
Oxford have emerged as clear favourites to win the Boat Race after more than 70% of bets were placed on the Dark Blues, according to bookmaker William Hill.
Spokesman Joe Crilly said: "Oxford are certainly the best backed crew as of yet, although that was very much the case at this stage of proceedings last year.
"Last year, however, we took nearly £40,000 on the day of the race and Cambridge became best backed by the time the race started. Maybe history will repeat itself this time around."