Lawrence Woodward, a former head of the SA, said grey areas in organic certification were allowing supermarkets to encourage producers to exploit them. He singled out organic poultry farming as an area where loopholes are regularly abused. Beak tipping, the use of conventional feed and the use of conventional chicks should be banned, said Woodward.
"It is completely against organic principles," he said. "If they're clipping beaks because there is a problem, those systems should not be allowed. It is a symptom of too high a stocking density.
"The Soil Association should take the lead, take the moral high ground and close the loopholes, the derogations," Woodward added.
But Robin Maynard, communications director of the SA, said it had the most rigorous standards of the organic certification bodies, 10 of which operate in the UK. "The Soil Association has always chosen to have a higher set of standards than the EU. The EU has a great interest in market trade and we don't want to become like the US, where standards have been dumbed down.
"Some supermarkets are seeking or choosing some certifiers who have lower standards on poultry and pigs," said Maynard, who acknowledged supermarket producers may be under pressure to "use methods that aren't sympathetic to organic principles" because their margins are so tight.
But a spokesman for Tesco said: "It is nonsense to suggest we are putting pressure on anyone to reduce standards."
Maynard defended the SA's record on poultry farming. Beak tipping is only allowed "if there is a welfare problem," he said. "If you've got severe pecking and/or cannabalism, and if a vet recommends it, we allow it."
The use of up to 15% non-organic feed for poultry and pigs is allowed if the farmer can show there is no alternative available, said Maynard. This will reduce to 5% by 2011.
"It's a cautious balance," said Maynard, between keeping the principles pure and putting "an awful lot of people out of business".