A report soon to be voted on by the European Parliament poses a significant new threat to vulnerable shark species, a coalition of green groups claims.
At issue is the mechanism for checking catches are legitimate
It fears changes will be made to EU legislation that aims to prevent the illegal practice of "finning".
This involves chopping off the valuable fins of sharks and then dumping their carcasses overboard.
The coalition says proposals to alter the way catches are monitored will be open to abuse.
It believes already weak legislation will be weakened even further, resulting in many more sharks being killed by European fishermen to supply the Chinese market with the primary ingredient for shark fin soup.
The soup is a delicacy which restaurants can sell for up to $100 a bowl.
"Finning is a major factor in the unsustainable mortality of shark populations," says the Shark Alliance, a union of environment groups who aim to promote science-based conservation of sharks.
At issue is the mechanism used by the authorities to determine whether vessel masters have landed a legal catch.
Fishermen are permitted to remove fins before returning to harbour to allow freezing of carcasses. The difficulty then arises of determining whether the weight of the fins landed corresponds to the weight of the carcasses landed.
The current regulations demand that the weight of fins as a proportion of the total catch does not exceed 5%. But Spanish MEPS have argued that this figure should be raised to 6.5% because the species of shark most often caught in European waters - the blue shark (Prionace glauca) - has relatively large fins.
They argue this means fishermen have to discard a portion of the fin to meet their legal requirements.
The conservationists, on the other hand, are concerned that new amendments would merely increase the potential for finning to go unpunished.
The Shark Alliance says the current 5% value, which is more lenient than that set by all other major shark-fishing countries, is already too high.
"If this recommendation was to be adopted by the Commission, it would allow for the finning of more than two out of every three sharks that are caught," says Sonja Fordham, the alliance's policy director.
"Sharks are in dire need of responsible management. The finning ratio clearly needs to be lowered and not raised."
Many shark species found in European waters have been classified as endangered or critically endangered by the IUCN-World Conservation Union.
Sharks are particularly vulnerable because their population growth is very slow, with some species not giving birth until the age of 20 or above.
One-third of all declared shark-fin imports to the Hong Kong market now originate from Europe, with Spanish fleets supplying more fins than any other EU country.
Fisherman are permitted to remove fins at sea, but not to dump bodies
Portugal, the UK and France have also made significant contributions to the trade.
The Shark Alliance also recommends that fishermen be forced to land fins and the carcasses from which they are claimed to have come in the same port.
"The EU is really having a wide-ranging negative effect on sharks around the world," says Fordham.