Australia opened its case against Japan at the International Court of Justice, arguing that Japan's annual hunt around Antarctica is an illegal commercial activity outlawed since 1986 by an International Whaling Commission moratorium.
Australia wants the court to issue a ruling banning Japanese whaling by the end of the year in time to stop the next whaling season.
The whaling fleet generally leaves Japan each December to begin harpooning whales in January in the Antarctic Ocean, where Australia declared a whale sanctuary in 1999.
Japan argues that the annual hunt is legal under article eight of the 1946 International Convention for Regulation of Whaling, which allows governments to grant permits authorizing their citizens "to kill, take and treat whales for purposes of scientific research."
Japan's government claims the research is needed to provide data on whale populations. Opponents say the program is a commercial whaling operation that sells the whale meat for consumption.
The vast majority of whales killed in the hunt are minke whales. It has an annual quota of around 900 minke whales. Japan has also harpooned a small number of fin whales.
Once a common item at dinner tables in homes and on school lunch menus, it is not as popular as it used to be because of the high price and the controversy.
The Sea Shepard conservation group has been conducting rallies to block the hunt. Their protests in recent seasons have spoiled Japan's whaling expeditions and hunting plans.
The group said it does not plan protests at the hearings. Two of its members have been granted seats at the hearings, said Geert Vons, a Dutch member of Sea Shepherd.
"With modern technology, it is not necessary to kill whales anymore," said Geert Vons.
The hearings are expected to last for 11 days, with New Zealand supporting Australia. A judgment will take months. The court's decisions are final and binding.