One consignment of the gourmet delicacy from waters around Barra have been destroyed after being intercepted in Argyll en route to Hong Kong.
The former British colony's government had previously warned about the import of certain razor clams from Scotland that were considered potentially poisonous.
The latest 815kg catch, worth about £40,000, was seized from a vehicle at Oban ferry terminal last month and has been destroyed.
Shellfish, such as the current consignment, farmed in unclassified areas are deemed unfit for human consumption and cannot enter the food chain. People who eat illegally harvested products may suffer nausea, blindness and in severe cases respiratory paralysis or death.
It is unclear whether any toxins were discovered in the consignment, which was caught by environmental health officers on February 27. Organised gangs are thought to harvest the products, which are said to be part of a wider problem.
Argyll and Bute Council said no shellfish from the consignment reached the market. A spokesman said there had been no prosecutions to date, but its long-term strategy of dealing with the problem was continuing.
Razor clams have a soft, sweet flesh much favoured by chefs and there is a lucrative market for them across Europe and in the Far East. They can be harvested using dredged suction pumps, or traditionally by hand.
Argyll and Bute councillor David Kinniburgh said: "The council is advising shellfish harvesters, processors and food businesses to ensure that any shellfish intended for human consumption should be harvested from approved waters and be accompanied by the appropriate documentation.
"There are significant risks attached to the consumption of unsafe shellfish.
"We aim to ensure products entering the food chain are safe and that we protect responsible businesses."
The Hong Kong government's Centre For Food Safety had previously had to warn about consignments of razor clams imported from Scotland that might be contaminated with phycotoxins, which are produced by small marine organisms, leading to diarrhetic shellfish poisoning.