The owner of an alpaca is seeking a judicial review to try to stop the animal from being culled.
The Department for the Environment, Food and Rural Affairs (Defra) ordered Geronimo be put down by the end of August after he tested positive for bovine tuberculosis (bTB).
Helen MacDonald, from Wickwar, South Gloucestershire, said she had "no choice" other than to take it to court.
She said "new evidence" showed the animal was healthy.
The fight to prevent the alpaca from being euthanized has so far taken more than a year.
Ms MacDonald's fight centres on her belief - supported by the British Alpaca Society - that Defra tests for bovine tuberculosis (bTB) are faulty and that six-year-old Geronimo is healthy.
She said she would seek a judicial review, in what has become a test case for the management of camelids in England and Wales.
"Killing Geronimo without a proper investigation and consultation between all stakeholders will ultimately not help to address the issue of proper TB management in this country," she said.
She said she would invite the government to consider "all the new evidence" in the "unique" case.
Ms MacDonald said Geronimo had been imported from New Zealand and had a monetary "value" of £30,000.
A crowdfunding campaign to cover the costs of a legal challenge has so far raised more than £6,000.
- Alpacas are members of the camel and llama family of mammals known as camelids
- Dromedary camels, Bactrian camels, llamas, vicuñas and guanacos are members of the same family
- Alpacas are domesticated versions of vicunas - South American ruminants that live high in the Andes, raised mainly for their soft wool
A month ago, Defra gave the alpaca a stay of execution, issuing a deadline for him to be culled by the end of August.
Defra's policy is to isolate and then euthanize any cattle, including camelids, which test positive for bTB.
In a statement, Defra has said: "The evidence that he is truly infected is substantial and we are confident this is the case."