Japan is at risk of losing its status as a Pacific Islands Forum Dialogue Partner over Tokyo's nuclear waste dumping plan.
Japan is due to start dumping one million tonnes of nuclear waste from the damaged Fukushima Daiichi nuclear power plant into the Pacific Ocean in only a few months.
According to Japan's government, the wastewater is to be treated by an Advanced Liquid Processing System, which will remove nuclides from the water.
It says the water to be discharged into the ocean is not contaminated.
Last year, the Pacific Islands Forum demanded Japan share pivotal information about the plan.
Secretary General Henry Puna said this month that, in order to keep its status, Japan needs to ramp up communication and transparency over the issue.
The message to Japan is, "hey look, has there been a change in your attitude to the Pacific?" he told RNZ Pacific.
"It's a bit daunting, talking to a big sovereign country like Japan, and also a good, long-standing friend of the Pacific," Puna said.
The "preferred course of action" is to engage in a "friendly manner" with Japan.
"We're long-standing friends, and Japan is a very important partner for us in the Pacific," he said.
"This issue strikes at the very heart of our being as Pacific people. We will not let it go.
"In fact, we are very serious and we will take all options to get Japan to at least cooperate with us by releasing the information that our technical experts are asking of them.
"Because all we want is to be in a position where our experts can say, 'okay, look, the release is harmless, you can go ahead', or 'there are some issues that we need further discussion and further scientific research with Japan'," he said.