Palau is alleged to be pledging to change the way it votes when the International Whaling Commission meets next week.
A Sunday Times undercover investigation found officials from six countries, including the Marshall Islands and Kiribati, willing to consider selling their votes on the IWC, something the Marshall Islands is denying.
Several Pacific countries including the Marshall Islands and Palau have supported Japan's stance at recent IWC summits.
Since the 1980s Japan has been the second largest aid donor behind the United States, the Marshall Islands' primary diplomatic partner.
Our correspondent in the Marshall Islands, Giff Johnson says Palau has a very similar aid relationship with Japan but says it intends to vote for a cutback in the killing of Minke whales.
"And it will be interesting to see whether there's any fallout from that and I suspect there won't be any in terms of the relationship between Japan and Palau. And that may then lead to some other islands taking a look and seeing maybe they do have some other options in how they might choose to make their government policy in a different way."