That, at least, is how the federal government sees it.
For years, the government has said the cats - said to be descendants of Hemingway's six-toed pet Snowball - are subject to federal regulation because the museum displays them in advertisements and charges admission to tour the grounds.
A federal appeals court recently agreed with the government, ruling that the U.S. Department of Agriculture has the power to regulate the cats under the Animal Welfare Act.
Museum Chief Executive Mike Morawski has his own view of the government's position. "It's absurd," he said.
Hemingway wrote several of his masterpieces at the Key West estate in the 1930s, and the cats have been a fixture there for generations. Many tourists come not just for Hemingway but for the 45 cats, many of which have extra toes.
The regulatory dispute goes back nearly a decade.
After receiving a complaint over the cats' care, a USDA regional director for animal care decided in October 2003 to label the museum an animal exhibitor.
Museum officials have said that at various times regulators sought to make them cage the cats in individual shelters at night, build a higher fence, erect an electrical wire atop the home's brick wall or hire a night watchman so the cats couldn't escape.
In 2007, a USDA representative said the agency wanted only that "enclosures be set up so other animals can't enter (the property) and the cats can't get into the street" - not that the felines be given cages.
Morawski said the museum installed mesh fencing several years ago to keep the cats in the compound, which satisfied the department's demands. The museum has remained "in compliance with all Animal Welfare Act regulations" since 2008, after it installed the fencing and passed an inspection, a USDA spokesman said in an email.
Still, the issue of jurisdiction did not go away.
In 2009, the museum challenged in federal court the agency's decision to label it an animal exhibitor.
On Dec. 7, an appeals court agreed with the USDA and a district court that the department can regulate the cats. What that means for the museum and the cats is unclear.
Morawski said the cats had always been well-tended, and a vet visits once a week. "This has never been an issue in relation to the care of the cats," he said.
Morawski described the USDA tactics as heavy-handed. "They came to our community, our local business, and said, 'Your state, city, county regulations are not enough,'" he said.
The judges who ruled in favor of the government - a three-judge panel of the U.S. 11th Circuit Court of Appeals - noted the museum's predicament.
"We appreciate the museum's somewhat unique situation, and we sympathize with its frustration," the jurists ruled. "Nevertheless, it is not the court's role to evaluate the wisdom of federal regulations implemented according to the powers constitutionally vested in Congress."
Aside from the years-long legal wrangling, there's another long-standing cat fight at the estate - this one regarding the felines' ties to the cat Snowball, said to be a gift to the writer when he lived in Key West.
"Papa never had six- and seven-toed cats when he lived" there, Hemingway's right-hand man, Toby Bruce, told Los Angeles Times reporter Charles Hillinger in 1972. "Papa had two cats for a brief period at the Key West home in the '30s. That was it."
The museum disputes that, as do some Hemingway aficionados.
As for the cats, they're not talking.
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