By the end of Tuesday 140,000 of the harp seals will have been killed, even though the sealers aren't allowed to kill the youngest animals, called "whitecoats".
Canada used to kill lots of seals but pressure from other countries forced them to cut back.
Now they're upping the number allowed to be killed again, to a million over three years.
Another problem is that some of the animal rights and environmental groups say they're not being allowed to check up on how the seals are being killed.
"This hunt is bigger than it's ever been," said Rebecca Aldworth, from the International Fund for Animal Welfare.