Humanoid robots are working in warehouses, undergoing tests for package delivery and folding laundry, but they can’t fly domestic, at least not on Southwest Airlines. The airline has a new policy that went into effect on May 15, banning humanoid robots and “animal-like robots” from being transported in airplane cabins or as checked baggage, regardless of size or purpose.

The airline does make an exception for other robots that don’t fall into those categories, but they must fit within a carry-on-size bag and comply with existing battery restrictions.

The airline’s restrictions on mobile power banks, which use the same kind of battery tech found in these robots, limit them to 100 watt-hours, according to the airline’s website. As of April 20, fliers can only bring one power bank per customer. Southwest began cracking down on batteries last year due to their potential to combust. Passengers aren’t allowed to charge devices in their carry-ons, either.

Lynn Lunsford, a spokesperson for Southwest, told CNET the change was not in response to any single incident.

“We have had a handful of recent experiences in which customers either bought seats for devices or tried to carry them on as baggage,” Lunsford said in an email. “One led to a flight delay, which has been making headlines. The primary concern is the size of the lithium-ion batteries used to power them and the risk they pose during flight. To eliminate confusion, the policy applies to all similar devices, regardless of size.”

Robots in the air

Southwest has been the subject of several robot incidents recently. Last month, a Bebop robot made by Unitree caused a flight delay at Oakland San Francisco Bay Airport when it was seated on a Southwest flight to San Diego as a passenger. The robot was apparently employed by a Dallas company that rents out humanoid robots for events.

Separately, a smaller robot called Stewie flew in its own seat on a flight from Dallas to Las Vegas on May 10. It was also owned by a company that rents out robots.