SAN FRANCISCO, CA - JULY 08:  United Airlines planes sit on the tarmac at San Francisco International Airport on July 8, 2015 in San Francisco, California. Thousands of United Airlines passengers around the world were grounded Wednesday due to a computer glitch. An estimated 3,500 were affected.  (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JULY 08: United Airlines planes sit on the tarmac at San Francisco International Airport on July 8, 2015 in San Francisco, California. Thousands of United Airlines passengers around the world were grounded Wednesday due to a computer glitch. An estimated 3,500 were affected. (Photo by Justin Sullivan/Getty Images)
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(CNN) —  

Sen. John Kennedy is calling out United Airlines, demanding an “immediate explanation” of the death of a dog on a flight this week, and saying other animals have suffered while in United’s care.

“For many people, pets are members of the family,” Kennedy writes in a letter sent today to the president of United Airlines, J. Scott Kirby. “They should not be treated like insignificant cargo. Frankly, they shouldn’t be placed in the cargo hold much less an overhead bin.”

The Louisiana Republican’s letter was prompted by the death of a French bulldog that has captured national attention this week. On Monday, on a flight from Houston to New York, the dog’s owners were told to put their pet inside an overhead bin. After the three-hour flight the dog had died.

Kennedy tweeted that he will file a bill Thursday to prohibit airlines from putting animals in overhead bins.

“I will be filing a bill tomorrow that will prohibit airlines from putting animals in overhead bins. Violators will face significant fines. Pets are family,” Kennedy wrote on Twitter.

United has apologized, say they assume “full responsibility” and have launched an investigation into what happened. A spokesman for United, Charlie Hobart, told CNN a flight attendant should not have told the passenger to put the dog in the bin used for carry-on bags. CNN reached out to United about Kennedy’s letter and has not yet received a response.

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But the incident has sparked new questions about United’s treatment of animals – especially in light of a US Department of Transportation report that was released last month about the number of animals that have died in the care of US carriers.

The report found that of the 24 animals that have died 18 did so while being handled by United. And of the 15 reported injuries of animals, 13 of those occurred with United.

“This pattern of animal deaths and injuries is simply inexcusable,” Kennedy writes. “I write to demand an immediate explanation for the number of animals who have died recently in United Airlines’ care.”

Kennedy spoke to reporters about his letter Wednesday, saying he was trying to be fair to the company but he’d run out of patience over the issue.

“They have some explaining to do,” Kennedy said. “I mean there are days up here on Capitol Hill I love dogs better than people. This isn’t something to joke about. What happened to this pet was disgraceful. I can’t imagine how the pet’s owner feels. But we need to get to the bottom of it. And I know we have many important things to do – but this is important too.”