* NMB ruling clears the way for union election
* IAM and AFA vying to represent flight attendants
* Shares up 7 cents at $23.06
CHICAGO, April 1 (Reuters) - The U.S. agency that mediates labor disputes set the stage on Friday for an election to determine which union will represent the more than 20,000 flight attendants at the newly merged United Continental Holdings (UAL.N), the unions said.
The National Mediation Board determined that United Continental, formed last year from a merger of United Airlines and Continental Airlines, has created a single transportation system for the purposes of negotiating with flight attendants.
The decision starts the clock for the NMB to set an election date for union representation. The NMB will set the date within two weeks.
The International Association of Machinists and Aerospace Workers, which represents more than 8,000 Continental flight attendants, and the Association of Flight Attendants, which represents about 13,000 United flight attendants, are vying to be the union for the merging worker forces.
United Continental still operates as two separate carriers and will do so until it receives a single operating certificate from the government. But the airline is already integrating its 87,000 employees.
Shares of United Continental were up 7 cents at $23.06 on the New York Stock Exchange. (Reporting by Kyle Peterson; Editing by Lisa Von Ahn)