American Airlines said on Friday that flights will be booked to full capacity starting July 1, meaning that passengers may notice more crowded flights as more people continue to travel.
Fort Worth, Texas-based American was previously limiting its seating capacity at 85% on each flight, or roughly 50% of the main cabin middle seats.
But airline executives have warned that underselling seats is not something they could do forever, particularly as they continue to bleed cash in the middle of the coronavirus pandemic.
American said it will notify customers if their flight is going to be full and allow them to move to more open flights when available.
U.S. airline passenger numbers have rebounded from lows reached in April, but executives and analysts have expressed concern about a spike in coronavirus cases in a number of U.S. states, including Texas.
Among measures to help people feel more comfortable about flying, American said it had teamed up with Vanderbilt University Medical Center to look into health and cleaning matters.
Starting June 30, it will begin asking customers during the check-in process to certify that they have been free of COVID-19 symptoms for the past 14 days.