Pro-whaling countries and chemical pollution are creating an increasingly bleak outlook for whales, according to campaigners.
Six cetacean species are critically endangered
The warning comes as delegates prepare for the annual International Whaling Commission meeting, starting on Monday.
The Environmental Investigation Agency wants to make pollution a priority at the meeting in Sorrento, Italy.
But it fears pro-whaling members who are threatening to create a separate alliance will dominate the debate.
A report by the agency highlights how susceptible whales, dolphins and porpoises are to toxic chemical pollutants. It also warns there are health risks to people who eat them.
"The threat of chemical pollutants to cetaceans is real," said the agency's Clare Perry.
"Combined with an increase in the number of pro-whaling countries joining the IWC, the outlook for whales looks increasingly bleak.
"All IWC member countries, whether they support commercial whaling or not, should consider the significance of environmental threats to whales, dolphins
Mercury, brominated flame retardants and polychlorinated biphenyls are among the toxic chemicals thought to cause disorders including reproductive failure, developmental problems and cancer.
The agency says mercury levels in canned whale stew in Japan are three times above permitted levels and exposure to the chemicals causes neurological damage.
The IWC has grown from 14 member states to 55 since it was set up in 1946 both to conserve whales and to develop the whaling industry.
WHALING SINCE THE BAN
The number of whales killed by Japan, Norway and Iceland since the IWC moratorium took effect in 1986 is 25,239
Most whales are killed with harpoons designed to explode inside them, though small traditional coastal communities use other methods
Average estimated time to death is more than 2mins, say opponents, with some whales taking over an hour to die
It imposed a moratorium on commercial whaling, in effect since 1986, to let whales recover from centuries of industrial whaling which had left some species near extinction.
Since then Japan, Norway and Iceland have killed 25,239 whales.
Six cetacean species are critically endangered and at least one, the Yangtze River basin dolphin, is in immediate danger of becoming the first cetacean species to become extinct as a result of human activity.
The warnings come as Japan has drawn up plans to replace the International Whaling Commission with a new pro-whaling alliance.
The IWC remains deadlocked between the countries opposed to a resumption of commercial whaling and those, led by Japan, which believe whale stocks can sustain limited commercial hunts.
Members of Japan's ruling party now say they are prepared to go it alone and describe the IWC as "totally dysfunctional".
Whalewatch, a coalition of 140 organisations, is lobbying the IWC to call a halt to all commercial and scientific whaling on welfare grounds.