If you're ever among the last to board a flight, as I often am, you're familiar with the sight of baby strollers, sometimes a dozen or more, parked in the jetway near the aircraft door. Long a tradition with family travelers, "gate-checking" strollers is commonplace on most airlines. Passengers often prefer to keep infants in their strollers until they enter the plane, leave the carriers with a crew member to be stored just before departure, and then brought back out onto the next jetway after arrival. But don't count on doing that with many types of strollers anymore if you're flying on American Airlines. Starting today, a new AA rule stipulates that "all strollers that are large, non-collapsible or over 20 lbs." must be checked at the ticket counter.

Here's how it breaks down: Lightweight, collapsible "umbrella" strollers can be gate-checked or taken on board if they fit in the overhead bins; they are exempt from carry-on allowance. Collapsible full-size strollers under 20 pounds can be gate-checked but cannot be taken onto the aircraft. Strollers that are large, non-collapsible, or heavy (more than 20 pounds) must be checked at the counter, before going through security. All checked strollers are exempt from baggage charges.

Smart Traveler Mark Orwoll is the International Editor of Travel + Leisure.