Fort Worth-based American Airlines says it will start booking flights to full capacity next week.
The move comes as the United States sets records for new reported cases of the coronavirus.
The airline will continue to notify passengers when their planes are full and allow them to switch to less crowded flights at no extra cost through Sept. 30.
Passengers with flights booked through Sept. 30 can also change their flights, including adjusting origin and destination cities, without incurring a travel change fee but will have to pay for any difference in the fare.
Delta and Southwest Airlines leave middle seats open or limit bookings to create space between passengers to minimize possible exposure to COVID-19.