Southwest Airlines believes the delta variant is the cause of a drop in demand.
The Dallas-based airline reportedly said in July was profitable, but it expects turning profits in the third quarter will prove to be more difficult.
According to CNN the airline expects September revenue to be down by as much as 25% when compared to the same month in 2010.
The airline is also reporting an uptick in cancelations, according to CNN.
Several other airlines are also concerned about profits.
Most airlines are taking measures to make customers and workers feel more safe.
Southwest Airlines does not have a vaccine mandate.
United announced it would require all employees to be vaccinated against COVID-19 by the fall.