The judges decided the price-fixing agreement between UK booksellers and publishers was not against European Union competition law, as the European Commission ruled in 1988.
The Publishers' Association, which brought the appeal, believes the Restrictive Practices Court will have to take the ruling into account when it re-examines the agreement in May.
It also claims it could result in the resumption of the Net Book Agreement in Ireland.
Late last year the association, which represents most leading British publishers, launched an appeal to raise £1m for legal fees to fight its case against the Office of Fair Trading. The move followed the decision last August by the OFT's director-general, Sir Bryan Carsberg, to ask the Restrictive Practices Court to investigate whether the agreement still operated in the public interest.
However, it is not just under a legal threat but a commercial one. Two big publishing houses, Hodder Headline and Reed International, have already pulled out of the voluntary agreement.
Booksellers that stock their books can now offer discounts. Sainsbury's is presently featuring 20 Hodder Headline paperbacks at a £2 reduction.
Tim Hely Hutchinson, chief executive of Hodder Headline, said he did not believe that the ruling would make a difference to its survival. "The European Union will not get involved for the time being in questions of whether each country should have a net book agreement. They're leaving it to the commercial realities.
"The situation remains that the net book agreement is unravelling.
``Two of the biggest UK publishing groups have denetted all their titles and a number of smaller publishers are already pulling out.''