Activists have released images that appear to show a Japanese ship with a dead minke whale on its deck, which they claim was caught and slaughtered within the sanctuary.
The international court of justice ruled in 2014 that Japan’s whaling in the Antarctic was illegal.
Japan says that they need to kill the mammals in order to study them for their scientific research.
“The Australian government is deeply disappointed that Japan has decided to return to the Southern Ocean this summer to undertake so-called ‘scientific whaling’,” said Josh Frydenberg, Australia’s environment minister.
The activists from marine conservation organisation Sea Shepherd say that the boat’s crew covered up the whale carcass and the harpoons when they saw their helicopter.