Animal welfare campaigners say Greenland's whaling, held under rules permitting subsistence hunting, has become too commercial in character.
The World Society for the Protection of Animals (WSPA) found that a quarter of last year's catch was traded for profit through a private food company.
International Whaling Commission (IWC) rules allow hunting where there is a nutritional and cultural need.
The IWC annual meeting gets underway next week in Santiago, Chile.
WSPA campaigners are presenting their report this week to a preliminary meeting of the organisation's committee on aboriginal (or subsistence) whaling.
"Greenland has been on the slippery slope towards commercial whaling for years, and now, demonstrably, they've crossed the line," said WSPA's marine mammals manager Claire Bass.
"The IWC has heard anecdotally about these processing operations, but this is the first time it's been quantified, so we're expecting it to be explosive," she told BBC News
Quotas for the five communities claiming a need for subsistence hunting were renewed at last year's IWC meeting in Anchorage, Alaska.
At the time, some delegates queried Greenland's plans to expand its hunt to include bowhead and humpback whales - two species it had not previously targeted - and noted allegations that whalemeat regularly changed hands for money.
IWC rules do not explicitly prohibit commercial trade, but they specify that permits are granted only "to satisfy aboriginal subsistence need".
Delegates eventually voted to allow the bowhead quota, but rejected the request for humpbacks. Denmark, which speaks for Greenland in the IWC, is bidding for humpbacks again this year.
Over the last 12 months, WSPA visited markets and harbours around Greenland. Investigators posed as a documentary film crew reporting on local traditions and culture.
They concluded that at least a quarter of the whalemeat landed around the coasts was traded through a single company, Arctic Green Food, with supermarkets the principal destination.
The company advertises packets of whalemeat for sale within Greenland on its website. Products include steak, mince, salted blubber, and cuts from the fins and tails of minke whales, as well as unspecified meat from fin whales.
Tonnes Berthelsen, managing director of Arctic Green Food, told BBC News his company traded meat from about 40 whales each year.
"We're selling it frozen; and if we didn't sell it like that, if people weren't able to buy it frozen, then the waste would be very high."
But whereas the IWC says that "the meat and products are to be used exclusively for local consumption", WSPA points out that because the meat is sold in supermarkets, anyone can buy and consume it, even foreign nationals, raising the question of whether there is a genuine nutritional and cultural need.
WSPA is one of the few groups to campaign against subsistence whaling.
Traditional whaling boat. Image: BBC
The majority of conservation organisations support it as providing a sustainable resource to communities that need the meat.
There was a tacit agreement among anti-whaling NGOs not to oppose the renewal of subsistence quotas at last year's IWC meeting, an agreement that WSPA did not support on animal welfare grounds.
"The record of these hunts is really bad," said Ms Bass.
"Only one in five whales dies within a minute. These are the worst whale hunts in the world on welfare grounds."
Records submitted to the IWC show that in 2006, fin whales took on average 35 minutes to die, with one taking nearly six hours. Norway's overtly commercial hunters, by contrast, kill the majority of their prey within one minute.
The IWC's various committees are coming to the end of their series of meetings in Santiago before the full organisation convenes on Monday.
Its week-long meeting is likely to be dominated by South American proposals for a whale sanctuary in the South Atlantic, and by discussions on whether pro- and anti-whaling blocs can find a path towards eventual compromise.