The woman and her squirrel were removed by police and caused a two-hour delay.
Passengers on a Frontier Airlines flight, in Orlando, were forced to disembark and reboard after police were called to remove a woman travelling with an emotional support squirrel.
The woman had previously told Frontier staff she was with an emotional support animal but did not tell them it was a squirrel.
Frontier does not allow "exotic" animals onboard, according to the airline's statement.
"The passenger noted in their reservation that they were bringing an emotional support animal but it was not incidated [sic] that it was a squirrel," the airline said in a statement to Orlando ABC affiliate WFTV.
"Rodents, including squirrels, are not allowed on Frontier flights."
After the woman refused to leave the aircraft, police were called and escorted her in a wheelchair through the terminal.
The footage of her leaving the plane showed her giving the middle finger and then the thumbs up.
US airlines have cracked down on what animals count as emotional support after a variety of animals were used throughout the year.
Under Frontier guidelines, effective 1 November, only a dog or a cat can travel as an emotional support animal.
Earlier in the year, a woman tried to bring a peacock on board a flight in New Jersey.