DALLAS, TEXAS — Southwest Airlines will no longer allow passengers to bring humanoid or animal-like robots onto its flights or as checked baggage, under a policy that took effect last week. The carrier cited the lithium-ion batteries used in such robots, which have been linked to fires onboard aircraft.

"To ensure compliance with our guidelines for traveling safely with lithium-ion batteries, Southwest clarified its baggage policy to include robotic devices." A spokesperson said the change was not in response to any single incident.

The policy defines a human-like robot as one designed to resemble or imitate a human in appearance, movement, or behavior, and an animal-like robot as one designed to resemble or imitate an animal in appearance, movement, or behavior. Such robots are prohibited from being transported in the cabin or as checked baggage, regardless of size or purpose. Other robots, including toys, may be transported if they fit within a carry-on size bag and comply with existing battery restrictions.

The update followed an incident in which a man brought a humanoid robot named Stewie onto a Southwest flight from Las Vegas to Dallas, purchasing a separate ticket for the robot rather than checking it as cargo. A separate Southwest flight from Oakland, California, was also delayed because of a robot.

On May 10, tech entrepreneur Aaron Mehdizadeh purchased a coach seat on the Las Vegas-to-Dallas flight for Stewie. Stewie is part of The Robot Studio, a Dallas-based company that rents robots for events such as weddings and conferences. The robot drew attention from passengers and flight crew and went viral after the flight.

"Most people were excited to see a robot flying and it provided so much entertainment," said Mehdizadeh, the owner of The Robot Studio.