FILE PHOTO: Southwest Airlines planes are seen at LAX airport in Los Angeles, California, United States, October 22, 2015. REUTERS/Lucy Nicholson/File Photo
FILE PHOTO: Southwest Airlines planes are seen at LAX airport in Los Angeles, California, United States, October 22, 2015. REUTERS/Lucy Nicholson/File Photo

Southwest Airlines warns workers of prospect of first involuntary layoffs in its 49-year history