The Football Association (FA) will consider disciplinary action against clubs whose supporters "engage in discriminatory behaviour", including 'rent boy' chants.
It has been a familiar occurrence in recent years at Chelsea matches for opposition fans to use the chant, which in January 2022 was defined as a hate crime by the Crown Prosecution Service.
The chant was audible during Manchester City's FA Cup third-round win against the Blues on Sunday at the Etihad Stadium, and City confirmed after the match they would be looking into the matter along with the FA.
A statement issued by the FA on Wednesday said it "strongly condemns all offensive, abusive and discriminatory chanting in football stadiums, and is determined to stamp this behaviour out".
Sunday's incident was the third of its kind in the space of a week, with the FA also investigating distasteful chants used by Nottingham Forest fans during their 1-1 Premier League draw against the Blues, and by Manchester United supporters during their FA Cup win against Everton, apparently aimed at former Chelsea boss Frank Lampard.
The statement continued: "Today, The FA has formally written to all clubs across the Premier League, EFL [English Football League], National League, Women's Super League, Women's Championship and Steps 2-4, to remind them that it can pursue formal disciplinary action against any club whose supporters engage in discriminatory behaviour, now including the use of the term 'rent boy'.
"This important step follows the recent successful prosecution of an individual by the Crown Prosecution Service for homophobic abuse, specifically relating to the term 'rent boy'.
"The FA has now informed all clubs that it considers the 'rent boy' chant to be a breach of the FA Rules.
"These rules apply to the conduct of supporters at both home and away fixtures, and clubs at all levels of English football have a responsibility to ensure their spectators behave appropriately when attending matches.
"The FA takes all allegations of discrimination extremely seriously and would encourage anybody who has been subject to, or a witness of incidents of discrimination, to report it to The FA, the club or the relevant authorities so it can be investigated thoroughly.
"Together English football can drive meaningful and positive change so that stadiums can be a safe and enjoyable environment for all."