PHOENIX - Frustrated by an internal dispute over seniority, pilots at US Airways ousted their union of 59 years yesterday and agreed to be represented by another group.

The rare decertification election, supervised by the federal National Mediation Board, gave the fledgling US Airline Pilots Association the right to represent the 5,300 pilots in US Airways' system and dismissed the Air Line Pilots Association as the pilots' bargaining agent. The new union's victory margin was slim, with the vote at 2,723 to 2,554.

The pilots' group was created and is supported mostly by pilots from US Airways who clashed with other pilots after their carrier was acquired in 2005 by America West Holdings Corp., of Tempe, Ariz.

Seniority is extremely important for pilots because it determines how much they are paid. Their place in the company pecking order decides what planes they can fly, what routes they will take, and when they can go on vacation.

As pilots gain seniority, they move up to flying larger airplanes and get hefty pay raises with each move.

Scott Theuer, a 737 captain based in Philadelphia and spokesman for the US Airline Pilots Association, said the group had been unhappy for years with the way the Air Line Pilots Association represented US Airways pilots, providing them contracts they considered inferior to other airlines'.

The final straw, Theuer said, was an arbitration process the pilots' union oversaw that resulted in many pilots with the old US Airways winding up lower on the seniority list than some from the former America West who had less time on the job.

Theuer said the new union had slightly more support from pilots for the old US Airways than those at America West, but that the desire for a change "was pretty much all over."

Pilots have said that disagreements over seniority led to shouting matches in airport terminals. Supporters of the rival unions have sent one another threatening e-mails, engaged in at least one shoving match, and called one another to the parking lot to settle their arguments.

Their struggles have become a cautionary tale as a new wave of merger talks sweeps through the industry.

Northwest Airlines Corp. and Delta Air Lines Inc. hoped their pilots would agree on seniority before announcing plans to join forces earlier this week. But Northwest pilots refused to go along, and the companies moved ahead without a pilot agreement.

In statements, the Northwest pilots said they were being asked to accept a seniority structure that would put them on a lower pay scale than Delta pilots.

US Airways Group Inc. said in a statement that its "position throughout this process has been that we'll honor the union representation choices made by our employees." It said the new group would "inherit the contracts currently in place for East and West pilots."

The company said it would "reach out" to the new pilot group for talks "toward a single agreement for our pilots."

US Airways has agreed to contracts with all its employee groups except pilots, flight attendants and baggage and ramp employees. The union representing baggage and ramp employees signed off on a tentative agreement last week.