The letter cited Caroline Kennedy's tweet about the hunt, which drew international attention -- and criticism -- to Taiji.
The trade agreement is being negotiated by 12 nations that altogether make up about 40 percent of global gross domestic product. Simmons said the signatories aren't against the trade agreement -- just the dolphin hunt, which was revealed in the Oscar-winning documentary "The Cove."
The full list of signees is as follows:
Sean Penn Mia Farrow Sam Simon Cher Moby Ann Wilson Emily Deschanel Ingrid Newkirk / PETA Diane Warren Courtney Love Captain Paul Watson Susan Sarandon Chris DeRose / Last Chance for Animals Jennifer Hudson Nick Cannon Melissa Carbone / TTO Productions Shannon Elizabeth Oliver Stone Trevor Neilson / Global Philanthropy Group Nathan Runkle / Mercy for Animals Ellen DeGeneres Gene Baur / Farm Sanctuary Ian Somerhalder Olivia Munn Kellan Lutz Shannen Doherty Charlize Theron Cameron Diaz Alicia Silverstone Channing and Jenna Tatum Woody Harrelson Pamela Anderson Sharon Lawrence William Shattner Tony Kanal Gwyneth Paltrow Jennifer Aniston Josh Grad Reverend Jesse Jackson