Chelsea have warned their fans over using the word "yid" during their game against Tottenham at White Hart Lane tomorrow.
The Blues travel to north London hoping for three points against their rivals that will take them to the top of the Premier League.
Tensions are likely to be running high ahead of the game with Spurs manager Andre Villas-Boas going up against his former mentor Jose Mourinho for the first time, but Chelsea have warned their fans not to get too carried away.
A statement on the club's official website read: "This Saturday we make the short journey across London to face Tottenham Hotspur, in what promises to be a passionate and exciting encounter."
"Your support is an inspiration to the players as we seek three important points. However, for a small minority of fans, matches with Spurs have also brought deeply unpleasant and unwanted anti-Semitic behaviour, which has no place in football or anywhere in society."
"Tottenham supporters using the 'Y' word as a form of identity is not an excuse for abusive chanting.
"All forms of discriminatory behaviour and language are abhorrent and this includes the 'Y' word.
"The Football Association reiterated in its directive announced earlier this month that the use of the 'Y' word in football stadiums is unacceptable and could amount to a criminal offence, and leave those fans liable to prosecution and potentially a lengthy Football Banning Order.
"This is fully supported by Chelsea Football Club. We have continuously worked to eradicate all forms of discrimination, both at home and away, and the diversity within our club is obvious to all. The players on the field, fans watching from the stands and the religious background of our directors and owner all illustrate a multi-cultural club of which we are very proud.
"We need your help to bring to our attention anyone taking part in anti- Semitic behaviour or any other kind of abuse."