The row over Japan's plans to hunt around 1,000 whales is growing, after America became the latest country to call for the hunt to be stopped.
Japanese boats have already set off on a five-month mission to kill around 1,000 whales for scientific study.
Among the animals targeted are 50 humpback whales, which haven't been hunted for 40 years.
Japan says the number of whales it will kill is too small to have a big effect on how many whales there are.
Other countries - including the UK, Australia and New Zealand - have told Japan that the hunt is a bad idea and shouldn't take place.
Which whales is Japan hunting?
900 Minke whales
50 humpback whales
50 fin whales
In the 1960s there were so few humpback whales left that a worldwide ban was put in place to stop them dying out completely.
Now Japan is allowed to hunt the humpbacks again, but only for scientific research.
But the meat from the whales that are killed for the research must be sold for people to eat , under rules set by the International Whaling Commission.
Japanese officials say that humpback numbers are now big enough to let the hunt go on.
In Japan children wave as the whaling ships set off
"Taking 50 humpbacks from a population of tens of thousands will have no significant impact whatsoever," said one.
He said scientists will learn lots more about the creatures by examining the dead whales.
US officials say the scientists could learn just as much about the whales without killing them.