The High Court has ruled the sale of birds as pets at the Parrot Society show in Stafford is unlawful.
The Parrot Society shows will continue despite the ban on sales
Animal welfare worker Malcolm Haynes, from Great Wyrley, Staffordshire, had opposed the borough council's decision to allow sales at last October's show.
It was ruled that laws preventing animals being sold in a public place also applied to a "concourse of buyers or sellers" such as shows.
The Parrot Society said this would not end other shows that it organised.
Mr Justice Walker stressed he was not declaring that anyone who had sold birds at the Stafford showground had committed an offence. Clarify law
He said the legal challenge should clarify the law, which was being applied differently in different parts of the country.
Lawyers for Malcolm Haynes, who runs an animal rescue and re-homing charity, said: "The implication of this is that all future pet fairs would be subject to criminal sanctions under the 1951 (Pet Animals) Act."
Activities at the show include exchanging home-bred birds, promoting bird welfare and conservation.
Parrot Society council member Colin O'Hara said: "We will organise our subsequent shows without these sales.
"We have every expectation that the shows will be as popular with birdkeepers and families as before."
In a separate ruling, the judge rejected Mr Haynes' contention that the Department for Environment, Food and Rural Affairs (Defra) could not issue a general licence under bird flu regulations for bird events, rather than issuing individual licences.