Two major airlines based in Texas are drawing a hard line between human and humanoid: American Airlines and Southwest Airlines won’t permit human-like or animal-like robots to board flights as passengers.

Fort Worth-based American and Dallas-based Southwest recently adopted bans on robotic passengers after two incidents in which human-like robots joined flesh-and-blood passengers on Southwest flights.

In May, Aaron Mehdizadeh, owner of The Robot Studio rental company in Dallas, was heading from Las Vegas to Dallas Love Field with 3.5-foot-tall Stewie, according to CBS News Texas. Rather than shipping Stewie as cargo, Mehdizadeh bought the robot its own seat using a type of ticket often purchased for fragile items such as wedding dresses and equipment.

But because Stewie was technically a carry-on item, the robot wasn’t supposed to occupy a seat, according to eWeek. Crew members wound up disconnecting Stewie’s battery and relocating the robot to a window seat before takeoff.

Mehdizadeh pushed back on Southwest’s stance regarding the battery, telling CBS News Texas that Stewie’s power supply is a standard battery that’s similar to one for a laptop.

Stewie isn’t the only robot making mischief in the skies. In May, a 70-pound, human-like robot named Bebop caused a stir on a Southwest flight from Oakland, California, to San Diego.

The robot prompted a nearly one-hour flight delay after crew members realized it violated restrictions on large carry-ons and raised concerns about the battery, San Francisco TV station KGO reported. Dallas-based Elite Event Robotics owns Bebop.

Southwest seized Bebop’s lithium-ion battery, but the airline did let Bebop take the San Diego-bound flight.

Southwest’s new robot policy prohibits human-like or animal-like robots from riding in an airplane cabin or as checked baggage, no matter their size or purpose. All other robots, including toys, must fit in a carry-on size bag and comply with battery restrictions, the airline says.

In a statement sent to CultureMap, a Southwest spokeswoman says the airline “has taken a strong stance on this issue and has led the U.S. airline industry with our battery policy.”

“The robot policy is a further evolution of a [safety] journey we have been on for several months. This move was not in response to any single incident,” the spokeswoman adds. “To eliminate confusion, the policy applies to all similar devices, regardless of size.”

Lithium-ion batteries can overheat, catch on fire, or explode on airplanes.

American’s new robot policy, which took effect Monday, August 17, is similar to Southwest’s. The policy prohibits human-like and animal-like robots from sitting in a purchased seat, being stored in an overhead bin or traveling as checked baggage. The ban applies to U.S., international, and regional flights.

“While there have been no known events involving this type of robot on any American flight, this policy was developed following a comprehensive review of safety risks associated with these devices, including the large lithium-ion batteries that power them,” the airline said in an internal memo obtained by the View From the Wing travel blog.

American gate agents have been told not to allow a passenger accompanied by a robot to board a plane or to let a robot travel as a checked item, the memo say.

If a robot is discovered after check-in, American employees are supposed to follow the Federal Aviation Administration’s “undeclared dangerous goods” procedures. These procedures cover hazardous shipments like lithium-ion batteries, explosives, flammable liquids, and compressed gases that lack required warning labels or shipping documents.

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This article originally appeared on CultureMap.com.