Australia has set a deadline for Japan to stop whaling in the Southern Ocean by November this year, or face legal action.
Prime Minister Kevin Rudd said on Friday he was still hopeful that talks with Japan would lead to a voluntary halt.
Foreign Minister Katsuya Okada of Japan is to visit Australia this weekend.
Despite a 1986 international moratorium on commercial whaling, Japan kills hundreds of whales each year, ostensibly for scientific research.
Mr Rudd told Channel 7 that Australia would "work with the Japanese to reduce, through negotiation, their current catch to zero".
He then added: "If that fails - and I'm saying this very bluntly... - if that fails, then we will initiate that court action before the commencement of the whaling season in November 2010."
Mr Rudd said that was the bottom line and Australia wanted to be very clear to the Japanese that that was what it intends to do.
The BBC reports Australia has made such threats before, but the timing and assertive tone of this statement gave the words added weight.
Mr Rudd is currently slipping in popularity polls and faces an election this year.