U.S. Open officials have warned players to be careful that their use of Twitter during the Grand Slam tennis tournament, which started Monday, doesn't violate the sport's rules against passing along insider information.

Advisories to players have been posted in lounges and other backstage areas at Flushing Meadows, N.Y., according to media reports. The signs remind competitors that tweeting information about matches and players could violate professional tennis' anti-corruption rules.

Players are banned from sending tweets during matches. The advisories, which started appearing at the tournament last week, also apply to coaches, agents, family members, and tournament staff.

The warning irritated player Andy Roddick, who won the Open in 2003. "I think its lame the U.S. Open is trying to regulate our tweeting. I understand the on-court issue, but not sure they can tell us if we can," he said on Twitter. "I definitely respect the rule about inside info and on court, but u would seriously have to be a moron to send 'inside info' through a tweet," said Roddick, who has more than 100,000 followers on Twitter.

Tweets are the mini-messages of no more than 140 characters that people on Twitter use to communicate with followers or to comment on others' postings. Roddick is not the only player to chat with fans on Twitter. Serena Williams also uses the service and has almost 1 million followers.

In 2008, tennis' four governing bodies adopted anti-corruption rules following reports of suspicious betting at tournaments. The organizations include the ATP and Women's Tennis Association tours, the International Tennis Federation, and the Grand Slam Committee.

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