Ellen DeGeneres is among those backing the effort to stop the Taiji dolphin hunt. Pic: AP.

WASHINGTON (AP) — A group of American celebrities and other activists want President Barack Obama to refuse to sign an international trade agreement until Japan bans the capture and slaughter of dolphins in the fishing town of Taiji.

Backing the effort are Oscar-winning performers Sean Penn, Cher, Susan Sarandon, Jennifer Hudson, Gwyneth Paltrow and Charlize Theron as well as TV stars Ellen DeGeneres and William Shatner, and many others.

(MORE: The Taiji dolphin hunt is Japan’s shame)

In a letter dated Wednesday that includes dozens of names, hip-hop producer Russell Simmons asks U.S. Ambassador to Japan Caroline Kennedy to urge Obama to make stopping the dolphin hunt a key factor in negotiations for the trade pact known as the Trans-Pacific Partnership.

The Oscar-winning 2009 documentary “The Cove” chronicled the dolphin roundup in Taiji. Fishermen defend the hunt as a tradition.