The carrier is dropping its guarantee to frequent flyers on short trips to cut costs. It will now award miles based on the number flown, not the 500-mile minimum, as had been their previous practice.
The move will affect everyone except "Elite" members, who are those who fly at least 25,000 miles a year.
Continental is making the same change, while United and US Airways made the move last year for all their mileage program members.
Travelers are urged to keep careful watch over their specific programs, and some experts recommend using accumulated miles sooner rather than later.