Australia is stepping up a diplomatic campaign to persuade Japan to drop plans to increase commercial whaling.
Anti-whaling groups say Japan already kills too many whales
Under an international agreement, there is a moratorium on the hunting of whales, but some can be killed for scientific research.
Opponents of whale hunting say Japan is exploiting this loophole, killing hundreds and selling the meat.
Japan is reported to have said it wants to kill nearly twice the number of whales it hunted last year.
Australian Prime Minister John Howard says he has written to his Japanese counterpart, Junichiro Koizumi, to say that new research methods make killing whales unnecessary.
Mr Howard told Mr Koizumi to expect considerable public concern around the world if whale killing was increased.
"There is clear evidence of the extent of public interest in the continued health and welfare of whales and considerable public concern could be expected, not only in Australia, but across the globe, were whaling to increase," he wrote.
But Japan's Fisheries Agency said the country would continue its whaling which it says is done for scientific research.
"Our position on research whaling will not change just because of foreign pressure," Takanori Nagatomo, deputy director at the Far Seas Fisheries Division of the agency, told the AFP news agency.
"We have been engaging in research whaling to collect scientific data so we can resume commercial whaling," he said.
Japan is expected to submit plans to increase whaling at the annual meeting of the International Whaling Commission (IWC) in South Korea next month, Japanese media have reported.
Japan's research whaling programme has caused controversy since its inception in 1987, just a year after the IWC banned commercial whaling.
Critics say that Japan is using the excuse of scientific research into whales as a pretext to continue selling, and eating, whale meat.
Whale meat is seen as a delicacy in Japan, and officials in Tokyo maintain that the tradition is an important part of the nation's cultural heritage.
Japan says it needs to kill whales to collect accurate data on whales' ages, eating habits and other details and to bolster its view that some whale species such as minkes are consuming vast amounts of fish stock.