Celebrity chefs Jamie Oliver and Hugh Fearnley-Whittingstall have called on the public to boycott some supermarkets over cuts to the cost of milk.
The serial campaigners, in a letter to The Times, described a move by "cynical" retailers to pay less for a litre of milk than it costs to produce as "shocking" and warned that the situation makes dairy farming "unviable".
However the British Retail Consortium (BRC) has argued that supermarkets pay well, according to the BBC, and said that other milk buyers should face scrutiny.
"Supermarkets are the wrong guys to target here," said Sarah Cordey of the BRC. "The fact is that the supermarkets are actually the best payers for milk.
"Eleven of the top twelve best-paying milk contracts in the country are all contracts that are paid by supermarkets. What I don't see protesting farmers or TV chefs doing is questioning the amount that the big buyers of milk, who include manufacturers and the public sector, are paying."
The letter by Oliver and Fearnley-Whittingstall comes as hundreds of farmers get set to protest cuts by processors of up to 2p a litre. Farmers for Action (FFA) said marches would be held later in Staffordshire, Somerset, Leicestershire and Yorkshire.
Andrew Hemming, the vice chairman of the pressure group, said: "We want all dairy farmers to receive a milk price which covers their production and allows them to make a small profit for them to be able to supply the country not only for the next six months but the next 20 years."
"We pay more for bottled water than we do for milk - yet water bubbles out of the ground, while milk comes from livestock, which need our care. How mad is that?" wrote Oliver - who spent 11 years promoting Sainbury's - and Fearnley-Whittingstall in their letter.
"It's time supermarkets stopped using milk as a loss leader. And if they won't take that initiative, then perhaps consumers will consider moving their custom from those who offer milk at crazy knockdown prices to those who will commit to giving dairy farmers a fairer deal."
According to the BRC, about half of the milk British farmers produce ends up as liquid milk in bottles and cartons and only part of that is sold in supermarkets. The remainder is believed to be sold by convenience shops, door-to-door or used in catering, schools and prisons.
It says dairy processors, manufacturers and the public sector should be held accountable in the same way as retailers.
Last week agriculture minister Jim Paice said he was close to getting agreement on a revised voluntary code for dairy contracts from milk processors, after which he hoped to see a "fair deal" for dairy farmers.
He said the average price of a pint was 49p, of which 16p went to the farmers, and the price cuts were "a massive burden for the vast majority of dairy farmers".
The comments by Paice came as Meurig Raymond, of the National Farmers' Union (NFU), warned that dairy farmers from across the UK had been "pushed to the brink" by cuts to the price of milk.
Price cuts were recently announced by four leading dairy processors, to be applied from 1 August.
Robert Wiseman Dairies and First Milk have both cut the pence per litre (ppl) price by 1.7; Arla Foods UK by 2.0 and Dairy Crest by 1.65. They blame falling commodity prices.
The NFU said that the cuts would be felt by 27% of producers, and impact on 25% of the milk market volume.
It said an average farmer, with about 150-200 cows, would lose about £37,000 in revenue from the combined effect of cuts in May/June and August.
Those cuts would not affect farmers supplying Tesco, Sainsbury's, Marks & Spencer or Waitrose as they are paid directly by the supermarkets.
By Janie Manzoori-Stamford
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