The death of a dog left in an overhead bin on a recent United Airlines flight was allegedly joked about by United crew members on another flight four days later, actor Graham McTavish claims

In a tweet on Friday night, the Outlander star tweeted that he was flying from New Orleans to Chicago on the first leg of a trip to Vancouver when he heard United employees “making jokes about dogs in the overhead.”

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“Sorry, but my journey with @united today was rubbish,” he said, adding that staff on his delayed flight from Chicago to Vancouver were “plain rude” throughout. “Just makes a bad experience worse guys.”

Reps for the actor did not immediately respond to PEOPLE’s requests for comment.

In a statement to PEOPLE, United spokesperson Maggie Schmerin confirmed the airline “reached out to our customer to get the facts and will investigate with everyone involved.”

Image zoom Graham McTavish Todd Williamson/Getty Images for Entertainment Weekly

United has been embroiled in controversy over the past year, stemming back to last April when a doctor was forcibly removed in Chicago from an overbooked Louisville-bound flight after he refused to give up his seat.

They’ve been blamed in a string of animal-related incidents during that time too, including the deaths of a famed giant rabbit and several dogs.

The latest was last Monday’s headline-making death of a 10-month-old French bulldog named Kokito — who, while traveling in his carrier, was placed in an overhead bin at the insistence of a flight attendant during a flight from Houston to New York City.

Image zoom United Airlines Robert Alexander/Getty Images

Kokito’s owner Catalina Robledo was flying with her two children, 11-year-old daughter Sophia Ceballos and her 2-month-old son. She originally stored the canine in his carrier under the seat in front of her and resisted the flight attendant’s direction to move both to the overhead bin at first, but ultimately followed the flight attendant’s instruction.

At the end of the flight, when Robledo went to retrieve her dog, who was heard barking at least 30 minutes into the flight, she discovered her pet had died during the trip.

Fellow passenger Maggie Gremminger told PEOPLE that Robledo was “absolutely shocked and heartbroken” upon discovering that the animal had died during the flight.

“A stranger offered to hold her newborn while she sat on the floor, there in the airplane aisle. She was holding her dog and rocking back and forth. Her daughter was also crying,” Gremminger explained of the scene. “People who could not see what was happening were confused as to what was going on. I tried to encourage people to let them off first but it was confusing and so we waited for the rows to filter out. It was absolutely horrible.”

United spokesperson Schmerin told PEOPLE in a statement that while Robledo did tell the flight attendant Kokito was in the carrier, “our flight attendant did not hear or understand her, and did not knowingly place the dog in the overhead bin.”

“As we stated, we take full responsibility and are deeply sorry for this tragic accident,” Schmerin added. “We remain in contact with the family to express our condolences and offer support.”

In the wake of the dog’s death, Division Chief Carvana Cloud confirmed in a statement provided to PEOPLE that the Animal Cruelty Division of the Harris County District Attorney’s Office in Texas was partnering with the Animal Cruelty Taskforce to launch an investigation into the dog’s death.

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The airline also announced it was making changes to its pet policy, specifically to rules regarding pet carriers.

According to United’s current pet policy online, non-service dogs are permitted in the cabin with a service fee of $125 as long as the dog “is in an approved hard-sided or soft-sided kennel. The kennel must fit completely under the seat in front of the customer and remain there at all times.”

“To prevent this from happening again, by April we will issue bright colored bag tags to customers traveling with in-cabin pets. This visual tag will further help our flight attendants identify pets in-cabin,” Schmerin said in her statement to PEOPLE.