(AP) -- Watch what you tweet. That's the message tennis authorities are delivering as the U.S. Open gets set to start Monday, telling players and their entourages to be careful about what they post on the social networking site Twitter.
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 signs, written by the Tennis Integrity Unit, point out that Twitter messages could violate the sport's anti-corruption rules.
"Many of you will have Twitter accounts in order for your fans to follow you and to become more engaged in you and the sport - and this is great," the notices read. "However popular it is, it is important to warn you of some of the dangers posted by Twittering as it relates to the Tennis Anti-Corruption Program Rules."
Andy Roddick, for one, is not a fan of the warning. In a tweet Friday night, the 2003 U.S. Open champion wrote that he thinks it's "lame the US Open is trying to regulate our tweeting.. I understand the on-court issue but not sure they can tell us if we can't do it on our own time ... we'll see."
He added in another tweet: "I definitely respect the rule about inside info and on the court, but you would seriously have to be a moron to send 'inside info' through a tweet."
Told of Roddick's comments, tournament spokesman Chris Widmaier said, "We agree with Mr. Roddick that it would be 'moronic' to provide what might be construed as insider information. However, in the age of new media, it is imperative to ensure the absolute integrity of the game."
Sports leagues and governing bodies are paying close attention as more and more athletes turn to Twitter to reach fans directly; some NFL teams, for example, urged players not to use it. But tennis appears to be the first sport openly concerned about Twitter's possible effect on gambling.
The signs at the U.S. Open say tweeting is not allowed on court during matches. They also warn about using Twitter away from the court, saying sending "certain sensitive information concerning your match or other matches and/or players should be avoided. Depending on the information sent out this could be determined as the passing of 'inside information.'"
The messages define that as "information about the likely participation or likely performance of a player in an event or concerning the weather, court conditions, status, outcome or any other aspect of an event which is known by a Covered Person and is not information in the public domain."
The warnings say they apply to players, coaches, agents, family members and tournament staff.
"We take our anti-gambling procedures very seriously, and we're in full agreement with this recommendation from the Tennis Integrity Unit," Widmaier said Friday.
Twitter, launched in 2006, first gained popularity as a way for fans to follow the thoughts and activities of celebrities via messages of 140 characters or fewer.
Several prominent tennis players are part of the trend, including defending U.S. Open champion Serena Williams (who has nearly 1 million followers) and Roddick (more than 100,000).
Athletes post everything from personal blog links to updates on their social lives to injury updates. That last category is the sort of thing that worries the world of tennis, which revamped its anti-corruption policing a year ago in the wake of an investigation into match-fixing.
Jeff Rees, whose name appears at the bottom of the signs posted at the U.S. Open, was appointed in August 2008 to run the Tennis Integrity Unit. That's also when tennis' four governing bodies - the ATP and WTA tours, the International Tennis Federation and the Grand Slam Committee - adopted an anti-corruption code to make sure the same rules and penalties are applied across the sport.
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