On Thursday, United Airlines announced it would cut 600 jobs after losing $723 million last year. 

"In December, I announced a 7 percent reduction in our officer headcount," Chief Executive Officer Jeff Smisek told employees in a statement. "Today, we announced a difficult but necessary 6 percent reduction in our management and administrative staff that will begin in early February."

United spokeswoman Megan McCarthy said employees had until January 31st to volunteer, and "layoffs of nonunion employees will occur if the target isn't met." The company "also hopes to meet its target by not filling open positions."