Chelsea and Manchester City are being investigated by FIFA over their recruitment of young players.
This is the third time football's world governing body has looked at Chelsea, and in 2009 they were banned from making signings for two years.
In May, the Premier League fined City £300,000 and banned them from signing academy players for two years.
FIFA has stringent rules in place for signing players under the age of 18 to prevent exploitation and trafficking.
When asked by BBC Sport about Chelsea and Manchester City, it confirmed an investigation was "ongoing".
City has no knowledge of an investigation and is adamant they have done nothing wrong, while Chelsea insists they "comply with all FIFA statutes and regulations when recruiting players".
In 2009, Chelsea was banned from signing players after being found guilty of inducing Gael Kakuta to break his contract with Lens, though the sanction was lifted on appeal.
They were also scrutinised last year for the 2014 signing of Bertrand Traore from Association Jeunes Espoirs De Bobo-Dioulasso.
City's punishment, meanwhile, came after they were found to have approached the family of two young players who were registered with other clubs.
They are also awaiting a verdict from the Court of Arbitration for Sport over their signing of 16-year-old midfielder Benjamin Garre from Argentine club Velez Sarsfield in 2016.
FIFA cleared City of Sarsfield's allegation that they were not allowed to sign the player because of his nationality, on the basis Garre had an Italian passport.
However, the club opted to take the matter further, and the case was heard at the beginning on July.
In January last year, both Real Madrid and city rivals Atletico were banned from signing players for two transfer windows after breaching FIFA rules relating to the signing of minors.
Real had the sanction halved on appeal but Atletico had theirs upheld by the Court of Arbitration for Sport.
FIFA'S rules on the transfer of under-18s
FIFA bans the transfer of under-18s to different countries unless they meet strict criteria. It brought in the rules to help protect children from exploitation and trafficking.
According to the world football governing body, Under-18s can only be transferred abroad if:
The player's parents move to the country in which the new club is located for non-footballing reasons.
Both clubs are in the European Union or European Economic Area and the player is aged between 16 and 18. Even then, the buying club must meet more criteria relating to education, training, living conditions and support.
They live within 100km of the club.
