The harrowing clip shows the “monster foxes” with huge rolls of fat folding over their bodies and almost covering their eyes.
The animals, which can weigh up to five times their natural weight, are being kept in small cages in the fur farms in Finland.
Animal rights activists said the foxes are being fattened up so fur farmers can make as much money as possible.
The Finnish group Animal Justice said it uncovered the practice in five farm across Ostrobothnia, western Finland.
Spokeswoman Kristo Muurimaa said: “The conditions these animals are in is the result of greed for profits.
“Bigger skin means more money for the fur farmer. The animals pay the price with suffering.”
Claire Bass, executive director of the Humane Society International (HSI), said the “unethical” industry had “hit a shocking new low”.
She added: “It is proof, if further proof were needed, that the fur industry is about profit and cares nothing for animal welfare.
“Consumers will be rightly shocked and disturbed by these hideous images, which underline yet again the need to turn our backs on fur for good.”
The UK banned fur farming in 2000 for being unethical, with the country’s last fur farm being closed in 2002.
Despite this, campaigners said Britain still imports “huge amounts” of fur from other countries.
More than £2.5million of fur articles are reported to have been imported into the UK from Finland in the past five years.
Humane Society International (HSI) has launched a campaign, Fur Free Britain, urging MPs to ban to all fur imports to the UK.
A spokesman said: “HSI UK believes that if fur farming is too cruel to be allowed in the UK, we should not be importing that same cruelty from other countries.
“Whilst a member of the European Union it would be extremely difficult for the UK to introduce a fur ban because fur farming is still conducted across many EU member states.
“But HSI UK believes that Brexit now provides Britain with the opportunity to see all fur imports banned.”