The Ernest Hemingway Home and Museum, where the writer lived and worked for 10 years, has been locked in a dispute over its feline residents with the US Department of Agriculture (USDA), which says the cats should be caged.

The federal government claims the museum is an "exhibitor" of cats and needs a special licence to keep them (find out more about the cats here).

However, the Key West city commission backed the Hemingway Home's claim that the cats are not exhibits and exempted it from a city law prohibiting more than four domestic animals per household.

The exemption, granted last week, states: "The cats reside on the property just as [they] did in the time of Hemingway himself.

"They are not on exhibition in the manner of circus animals. The city commission finds that the family of polydactyl Hemingway cats are indeed animals of historic, social and tourism significance ... an integral part of the history and ambiance of the Hemingway House".

The UDSA was not available to comment on the city commission's ruling.

The museum is home to around 50 cats descended from a six-toed cat called Snowball, given to the Nobel prize-winning author by a ship's captain in the 30s.

The legal dispute began in 2003 after the Florida Keys Society for the Prevention of Cruelty to Animals raised concerns about the cats' welfare with the federal government, the Miami Herald reported.

The 1966 Animal Welfare Act requires a licence for zoos, circuses and magicians or anyone who used animals in their acts or advertisements. The six-toed cats feature prominently on the museum's website, but do not perform.

In January, the museum took the USDA to court in a bid to end the dispute, but the judge ruled that the two sides should reach an agreement.

The department and the museum are due in court again once a cat behaviour expert has assessed the felines later this month, the Miami Herald said. All the animals carry the gene for six toes, but not all display the trait. Normal cats have five front toes and four back toes.

Around half the cats at the Hemingway house are polydactyl, meaning they have extra toes. They sometimes appear to be wearing mittens because they seem to have a thumb on their paw, according to the museum.

Hemingway worked on the novel For Whom the Bell Tolls and short stories including The Snows of Kilimanjaro while he lived at the house, at 907 Whitehead Street in the heart of Old Town Key West.