Scientists say they have found clear evidence that meat from whales caught by Japan is being illegally sold in restaurants in the United States and South Korea.
Trading in meat from whales in danger of extinction is banned between countries that have signed the Convention on International Trade in Endangered Species.
The BBC reports commercial whaling has been frozen by an international moratorium since 1986.
But Japan is allowed to kill several hundred whales each year under an exemption for what is termed scientific research.
The meat from these whales is then sold in shops and restaurants there.
A genetic analysis of meat found in Los Angeles showed that it was identical to meat from a sei whale being sold in Japan in 2007.
Criminal proceedings have started against the Los Angeles restaurant caught selling the whale meat. It has now closed, but the chef and the owners face heavy penalties.