ORLANDO, Fla., Jan 11 (Reuters) - AirTran Airways, a unit of AirTran Holdings (AAI), said on Friday that a group of its ground workers had rejected a representation bid by the International Brotherhood of Teamsters union. AirTran said that it had been informed by the National Mediation Board, the federal body which monitors union elections, that the Teamsters Local 528 received only 33 percent of total votes from ballots counted. The airline said that the union needed 50 percent plus one vote for a successful bid to represent the workers. The Teamsters union, which already represents the airline's mechanics, had also sought to represent 1,731 AirTran customer service, ramp and reservations agents. AirTran shares closed down 22 cents, or 3.01 percent, to $7.10 at the close of Friday trading on the New York Stock Exchange.