US Open players and their entourages are being told to be careful about what they post on their Twitter accounts. Signs are being posted in the players' lounge, locker rooms and referee's office at the USTA Billie Jean King National Tennis Center with the header: "Important. Player Notice. Twitter Warning".
The message from the sport's Tennis Integrity Unit points out that Twitter messages could violate the sport's anti-corruption rules.
The signs say tweeting is not allowed on court during matches. They also say tweeting certain things off the court could be considered relaying inside information.
The warning applies to players, coaches, agents, family members and tournament staff.