Federal District Court Judge Richard Jones did not give a reason for denying the preliminary injunction sought by Japan's Institute of Cetacean Research against the Sea Shepherd Conservation Society, Oregon Public Broadcasting reported.
Sea Shepherd, based in western Washington, has led harassment campaigns against the Japanese research ships in Antarctica, hurling acid and smoke bombs at the group for killing whales, The (Portland) Oregonian reported Wednesday.
Gavin Carter, spokesman for the Japanese group, said he was disappointed with the judge's decision not to stop Sea Shepherd's actions, OPB said.
"At the end of the day, you can't have lawlessness on the high seas. You can't have anarchy on the high seas," Carter said.
Dan Harris, Sea Shepherd's lawyer, said the killing of whales is not legal.
"If a heroin dealer came to federal court and sought an injunction to be able to continue to sell their heroin in a particular neighborhood without interference from anyone, I have no doubt that the court would turn them down," he said.