The airline announced passengers will be charged $35 for use of the overhead bins.
The charges are slated to begin with flights booked on Wednesday. Online bookings will be charged less, according to Allegiant, but the price had not yet been set.
Passengers will be allowed to carry a smaller bag for free, such as a briefcase or purse that can fit under a seat.
Allegiant Air is a low-fare carrier specializing in smaller city destinations like Orlando and Las Vegas. It charges extra fees for services like early boarding and checking bags, similar to many airlines in the current market.
Allegiant carries less than 4 percent of the traffic of United or Delta.
The Associated Press contributed to this report.