A woman has slammed a US airline after they allegedly booted a three-year-old autistic boy off a flight because he would not wear a face mask.

Alyssa Sadler booked a Southwest Airlines flight from Midland in Texas to Houson with her son and one-year-old daughter when the incident occurred.

According to CNN, the flight started taxiing away from the gate before returning when the young boy would not keep his mask on.

“He was screaming. He was throwing a fit. He was screaming ‘no, no, no’,” Ms Sadler recalled.

“They’re going over the security safety features and all that, and the flight attendant walks by and tells me that he has to put a mask on.”

“So, I try to put the mask on him. He is three and has autism and sensory processing disorders, so he wouldn’t keep the mask on.”

Southwest airlines has a strict mask policy in place, which means all passengers over the age of two need to wear a mask or some form of face covering throughout the duration of the flight.

Since July 27, the airline has enforced a “no exemptions” policy unless the passenger is below the age of two, and that anyone who is not able to comply with the rule will not be unable to be transported by Southwest.

Southwest CEO Gary Kelly emphasised the no-exceptions policy because that “exception” could be someone carrying the virus.

“I’m very empathetic. I’m a grandfather. I have small grandchildren and I know how kids can be, but it’s just a matter of making sure that it’s a safe environment for everyone including all those families,” he said.

The airline’s official policy states that “if a customer is unable to wear a face covering for any reason, Southwest regrets that we are unable to transport the individual. In those cases, we will issue a full refund and hope to welcome the customer on board in the future, if public health guidance regarding face coverings changes.”

Ms Sadler claims a flight attendant alerted the captain of the three-year-old not wearing a mask, who then announced the reason for the early return over the loudspeaker.

Ms Sadler claimed the captain referred to her son as a “non-compliant passenger” and, according to Fox News, resulted in an escort helping to remove her family’s luggage.

“I agree with the mask policy,” Ms Sadler told local media outlet KTRK.

“I wear my mask everywhere I go. It’s not an issue, but you’ve got to have some kind of exemption, especially for people with disabilities.

“No three-year-old, who is autistic and has sensory processing disorder, is going to put anything on their face. He’s supposed to wear glasses. I can’t even get him to wear his glasses to help him see. He just doesn’t understand. He doesn’t like things touching his face, so he’s not going to put a mask on.”