United Airlines found itself in hot water once again after a Houston family blamed the airline for the death of their 5-year-old dog, who was put in the cargo hold of a plane that was delayed at the airport in Houston, according to ABC13.

The Rasmussen family claimed the dog, a King Charles Spaniel, was in the cargo hold while the plane stayed on the tarmac for two hours before it took off to San Francisco, the ABC affiliate report also said. 

The family said the dog died while it was held in the hold.

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"We are so sorry to learn of Lulu's passing and have reached out to our customer to offer our condolences and assistance. We are deeply upset any time an animal suffers an injury while traveling with us and especially grieved in the rare instance that one passes away. We are conducting a thorough review of this incident," the airline said in a statement to International Business Times. The statement didn't reveal the cause of the dog's death.

United Airlines had the worst record in pet deaths among airlines in the U.S. in 2016.  According to the Department of Transportation’s Air Travel Consumer Report, nine pets — eight dogs and a Sphynx kitten — died under the airline's care in 2016.

"More than 300 animals have died in cargo holds since 2005, including 74 on United flights. According to a report from the U.S. Department of Transportation, the airline had the worst record of animal deaths and injuries among all U.S. airlines in 2016," a PETA blog post also noted.

Over the last few months, United Airlines has found itself in a slew of controversies, with some linked to animals.

In April, a 10-month-old Continental Giant rabbit named Simon died on a United flight from the United Kingdom to the U.S. The animal was the offspring of the Guinness World Record-holding rabbit, Darius. Simon was found dead after arriving at the O’Hare airport, and the airline was blamed for its death as the rabbit was said to be in a healthy condition prior to boarding the plane. 

PETA’s president, Ingrid Newkirk, issued a statement following Simon’s death.

“This rabbit was failed first by the breeder – who churns out and sells baby bunnies when animal shelters and rescue groups are full of homeless rabbits – and then by United Airlines, which shipped him off in a cargo hold like an old suitcase,” Newkirk said.

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“This rabbit’s death is not unique – more than 300 animals have died in cargo holds since 2005, and many more have been injured or lost,” Newkirk continued in her statement. “PETA urges United to join JetBlue and Southwest in prohibiting companion animals from being flown as checked baggage in the confusion, noise, extreme temperatures, and improper pressurization of a cargo hold.”

Last month, rapper ScHoolboy Q accused United of putting his dog in a wrong flight. The rapper, whose real name is Quincy Matthew Hanley, asked the airline for an explanation on Twitter, adding he was "pissed" due to the incident and planned to sue the airline.