A European Union court has today ruled against member countries which operate minimum pricing policies.
The Court of Justice of the European Union upheld an earlier opinion that setting minimum prices for tobacco in Ireland, France and Austria is against EU directives.
The move calls into question the SNP's proposed policy on minimum alcohol pricing.
The Scottish Government said the decision has no bearing on its pricing plan but opponents argue that the ruling is a serious setback.
Gavin Hewitt, chief executive of the Scotch Whisky Association, said: "Given this latest evidence, the Scottish Government must now recognise the legal realities.
"It cannot introduce a trade barrier in breach of the UK's European obligations by imposing minimum pricing on alcohol in Scotland."
The pricing plan is part of the Alcohol Bill going through the Scottish Parliament. It is widely backed by health professionals and aims to tackle the country's damaging relationship with drink.
Ministers have not yet said what the proposed minimum price will be but 40p per unit has been used as an illustration.
Labour health spokeswoman Jackie Baillie said the court's decision confirmed her fears over the legality of the SNP's plan.
She added: "The Scottish Government has repeatedly refused Labour's requests to share the substance of their legal advice on minimum pricing.
"We can only assume that ministers have failed to clear up doubts over their plans because they have something to hide.
"Minimum unit pricing is the wrong policy but it now looks increasing likely that it is also legally incompetent."
A Scottish Government spokeswoman said: "We have already made clear that this long-running case concerns tobacco and a specific directive on tobacco.
"It does not relate to minimum pricing for alcohol. We consider that the introduction of minimum pricing for alcohol is capable of complying with European law."