The Dallas based carrier is suing one union for failing to stop mechanics boycotting overtime.
It has filed a lawsuit against the Aircraft Mechanics Fraternal Association and a number of union officials.
Southwest alleges the union did nothing to prevent mechanics collectively declining overtime work, forcing the airline to bring in external mechanics to keep up with maintenance schedules.
That has resulted in higher costs for the airline, the lawsuit says.
The number of mechanics signing up for overtime shifts dropped by 75%, Southwest claimed.
The union’s national director Brett Oestreich, who is named as a defendant in the suit, rejected Southwest’s claims, adding that the union did try to stop the overtime boycott.
The union represents about 2,400 Southwest mechanics.
Oestreich says the legal action is just a ploy to press the union to accept more outsourcing of maintenance functions.
Southwest said the overtime ban did not affect any flight operations.
