American activists and celebrities including Sean Penn and Gwyneth Paltrow, are urging US President Barack Obama not to sign an international trade agreement with Japan until the country bans the slaughter of dolphins.
Among those who have joined Penn and Paltrow to sign the letter written by hip-hop producer Russell Simmons, are Susan Sarandon, Jennifer Hudson, Charlize Theron, and TV personalities Ellen DeGeneres and William Shatner.
Mr Simmons claims that more than 600 dolphins have been slaughtered since the hunting season began in the fishing town of Taiji, on 1 September last year.
Anti-hunt activists have also reported that dozens of fishermen helped to herd about 250 dolphins into a cove one day in January.
Of those, about 40 were eventually killed for their meat. At least 50 others were kept alive for sale to aquariums and others, while the rest were released.
Warning: graphic content. Japanese fishermen round up and kill dolphins in the now infamous Taji cove
The 2009 Academy Award-winning documentary The Cove raised awareness and sparked protests against the annual hunt and ensuing slaughter in the town.
Japanese law currently allows a hunting season for dolphins, something that fishermen defend as a tradition.
The letter, dated Wednesday 5 Febraury, asks for the US ambassador to Japan, Caroline Kennedy, to persuade President Obama not to sign the Trans-Pacific Partnership (TPP) until Japan halts the practice.
The TPP is being negotiated by 12 nations that account for about 40 per cent of global GDP.
Ms Kennedy recently tweeted that she was deeply concerned by the tradition. Following the post, a US State Derparment spokeswoman said that the US was "concerned with both the sustainability and the humaneness of the Japanese dolphin hunts."
Mr Simmons' stressed that the signatories do not oppose the TPP, but want to see the dolphin hunts become a key factor in negotiations.
The letter said that corporations have spent the past two years crafting language in the TPP "to serve their interests."
"Should human compassion not be afforded the same privilege as business interests?" the letter asked.
It added: "The world is looking to you, Ambassador Kennedy, and to our government to send a clear message to Japan that this atrocity must be banned now."
Additional reporting by AP
Annual dolphin hunt in Taiji, Japan
Annual dolphin hunt in Taiji, Japan
1/15 The annual dolphin hunt in Taiji, Japan
A bottlenose dolphin was seen floating on back before slaughter
2/15 The annual dolphin hunt in Taiji, Japan
Fishermen hiding their culture and tradition
3/15 The annual dolphin hunt in Taiji, Japan
Remaining pod swims just a few feet from the slaughter of their family
4/15 The annual dolphin hunt in Taiji, Japan
Dolphin drive out to sea
5/15 The annual dolphin hunt in Taiji, Japan
Lathered in blood, fishermen receive more transfers of dolphin carcasses
6/15 The annual dolphin hunt in Taiji, Japan
Fishermen enter the cove just after sunrise
7/15 The annual dolphin hunt in Taiji, Japan
A juvenile Bottlenose barely surfaces during drive out. The chances of survival are slim after 5 tormenting days in the cove
8/15 The annual dolphin hunt in Taiji, Japan
Cove Guardians Jac and Ian document the slaughter
9/15 The annual dolphin hunt in Taiji, Japan
SSCS Cove Guardian Leader Melissa Sehgal interviews for CNN
10/15 The annual dolphin hunt in Taiji, Japan
Fishermen in wetsuits hunt dolphins at a cove in Taiji, western Japan; U.S. ambassador to Japan Caroline Kennedy has expressed deep concern over the traditional dolphin hunt. Local fisherman corral dolphins in a secluded bay before killing many for meat
11/15 The annual dolphin hunt in Taiji, Japan
The selection process of dolphins, during the annual dolphin hunt in Taiji. With 250 dolphins, this was the largest round-up in years
12/15 The annual dolphin hunt in Taiji, Japan
The agitated dolphins in the cove during the selection process. According to Sea Shepherd, Japanese fisherman rounded up more than 250 dolphins, including babies and juveniles
13/15 The annual dolphin hunt in Taiji, Japan
Japanese fisherman are shown in the cove. Taiji town claims the hunt is an important ritual dating back centuries
14/15 The annual dolphin hunt in Taiji, Japan
A rare albino calf swims close to his/her mother as the pod was herded into the cove. Dolphins captured in the cove are either sold into captivity, or slaughtered and sold for consumption, despite pleas from animal conservationists around the world against the event
15/15 The annual dolphin hunt in Taiji, Japan
The process of selecting dolphins during the annual cull, which the mayor of the town defends 'on scientific grounds'