"I mean, it's really sad", said Pattie Jirakll, an animal activist. "We provide compensation to all customers on board for the diversion".
It's the third headline-grabbing incident involving a canine for the company in just a week, after a puppy died in an overhead bin and another dog was accidentally sent to Japan instead of Kansas.
The French bulldog that died on the Houston to LaGuardia flight, named Kokito, was a gift to 11-year-old Sophia.
"Pets are not luggage, and they should not be put in the overhead compartment", she said. United said there was a miscommunication between the flight attendant and Kokito's owner. The airline mixed up two dog carriers in the cargo holds of two different flights.
United Airlines released a statement apologizing and taking full responsibility for the incident.
This legislation would ban dogs from being placed in overhead bins and it would ensure they have access to food and water. We remain in contact with the family to express our condolences and offer support.
The airline added that by April, it will begin issuing bright-colored bag tags to travelers flying with pets.
Data from the US Department of Transportation shows that three times as many animals died on United flights previous year than on all the other US carriers put together.
Kokito's death was not the first time United was involved in pet-related deaths.
John Kennedy, a Republican senator from Louisiana, is also demanding an explanation from United on its high rates of animal deaths in transit.