The star of Oscar-winning documentary The Cove, about a dolphin-killing village in Japan, has been detained by immigration authorities at Tokyo's Narita international airport.
Ric O'Barry, the former dolphin trainer for the Flipper TV series, said immigration officials told him he was not a tourist, the visa he was using to enter Japan, according to his lawyer, Takashi Takano.
He said officials accused Mr O'Barry of having close ties with the anti-whaling group Sea Shepherd, which Mr O'Barry denies.
Immigration officials said it is their policy not to comment on individual cases.
Mr Takano said he appealed against Mr O'Barry's detention, and that the Japanese government will decide on whether to allow Mr O'Barry into the country or deport him. The timeframe for that decision was not clear.
The Cove, which won the 2009 Academy Award for best documentary, shows dolphins being herded into a cove in the fishing village of Taiji and bludgeoned to death.
"The Japanese government is cracking down on those who oppose their war on dolphins," Mr O'Barry said in a statement sent by email to the Associated Press through his son, Lincoln O'Barry.
Officials in Taiji, a small fishing village in central Japan, and fishermen have defended the hunt as tradition, saying that eating dolphin meat is no different from eating beef or chicken.
Most Japanese have never eaten dolphin meat, and many say they are horrified by the dolphin-killing, and have joined the campaign against the Taiji hunt. Animal welfare activists say the dolphin hunt is driven mostly by the lucrative sale of dolphins to aquariums, with the meat sale income coming as a smaller extra.
Mr O'Barry has been stopped and questioned at Japanese immigration before, as well as temporarily taken into custody by local police on the suspicion of not having proper travel documents. But this is the first time he has been detained in this way.
He has the support of high-profile celebrities, including Sting, US Ambassador to Japan Caroline Kennedy and former Guns N' Roses drummer Matt Sorum.