Both the Air Line Pilots Association and the Association of Flight Attendants, which represent employees at both companies, have policies that call for the unions to negotiate their own agreements for integrating seniority lists. If the groups can't reach an agreement, an arbitrator would devise a solution.

Among the ways that the seniority of many employees may be protected is for the groups to agree to "fence off" certain pilot and flight attendant bases such as Philadelphia and Phoenix, preventing senior workers from other bases from bumping more junior employees out of their jobs, union officials said.