The decision by Marks & Spencer and Tesco is a serious blow to the confidence of the Shetland fish farming industry, even though the two firms buy only a tiny fraction of the pounds 30m-worth of salmon produced there annually.
Marks & Spencer, which has established a reputation for high-quality food, was the first to announce the suspension as 'a temporary precautionary measure'.
A spokeswoman said: 'Only a very small proportion of our salmon comes from the Shetland Islands, we buy most of it in western Scotland. We will not buy any more in Shetland until the situation has clarified.
'Our buyers are going to visit local farmers in the next few days to get first hand knowledge of the situation.'
She was not able to put a value on the store's annual salmon purchases in the Shetland Islands.
Shortly afterwards Tesco, which had originally said that it would continue buying salmon from the Shetland Islands, issued a statement saying that purchases would be suspended because of the pollution.
Like Marks & Spencer, Tesco gets only a small proportion of its salmon from Shetland. Sainsbury's and Safeway said last night that they would continue to buy from the islands but were monitoring the situation.
Safeway, which has sent a senior food technologist to the islands, said in a statement: 'The majority of our Shetland suppliers are not affected because they are nowhere near the location of the oil pollution.'
Yesterday's declaration of a fishing ban around the south of Mainland will put some salmon farms out of action anyway. Sixteen of the 61 farms with about 20-25 per cent of the fish are in the zone.
The remainder are further away, and the decision by Tesco and Marks & Spencer is a further blow to a local economy which has been devastated by the wreck of the oil tanker on Tuesday.
Scott Findlay, spokesman for the Shetland Salmon Farmers Association, said last night: 'The sooner we can get the buyers up here to talk to the salmon farmers and see that everything is all right the better. There is no pollution of salmon here yet, not one fish has been killed.'
One salmon farmer yesterday blamed media publicity for the stores suspending purchases, but said other customers were still buying locally.
Agust Alfredsson said: 'The French for example are taking a very sensible attitude. Some companies there have said they accept it is media hype and know that we have strict internal quality control.'
Both the oil and the dispersants sprayed to break up the slicks can make the fish unfit to eat. But Mr Findlay said that, at the request of farmers, dispersants had not been used near salmon cages.
Brian Wilson, Labour's transport spokesman, yesterday called on the Government to 'stop equivocating' about compensation for victims of the tanker disaster and make a clear-cut statement that local people will not suffer loss.