Mechanics for Southwest Airlines and its AirTran Airways subsidiary have approved a deal for combining the two groups' seniority lists.
The vote announced Thursday is a step toward forming a single workforce.
Dallas-based Southwest Airlines Co. bought AirTran in May 2011. Southwest currently is operating AirTran separately.
The Aircraft Mechanics Fraternal Association says the agreement included a timetable for Southwest to add a fourth line for maintenance work at Dallas Love Field. The deal also provides protection to prevent union members in Baltimore and Orlando, Fla., from being bumped in seniority.
AMFA represents about 1,750 Southwest employees. The roughly 500 mechanics at AirTran are represented by Teamsters Local 528.