A new list of corporate tax havens has named Jersey as the seventh most "aggressive" in the world.
The Tax Justice Network created the ranking by assigning a "haven score" based on 20 different criteria.
Both Jersey and Guernsey scored 98 out of a possible 100, putting them "up there with the worst".
The top three are the British Virgin Islands, Bermuda and the Cayman Islands, with Guernsey in 15th place and the Isle of Man in 17th.
A spokesperson for the Government of Jersey said they were "fully compliant" with standards set by "independent global bodies".
Jersey was higher than Guernsey because of a larger volume of foreign direct investment.
A spokesperson for Guernsey's government said the index "lacks credibility" and the island is "part of the solution in the fight against financial crime".
The Tax Justice Network is calling for a shift towards "unitary taxation", which would mean corporations are taxed where they do business rather than where they have headquarters.
John Christensen, a director at the pressure group, said the proposals represented "radical departure", but that he felt there is growing recognition of a need for change.
He also said that the Channel Islands must "take account" of the shift as they could be left "high and dry".
The new index contradicts the European Union's removal of the Channel Islands from their tax haven "grey list" in March.
However Mr Christensen said that the EU system was "flawed from the start", and that they would not blacklist it's own members or their dependencies.
An EU Commission spokesperson said that, by international standards, no member state can be described as a tax haven and the criteria for non-EU countries is the same.
Their process had proven to be a "true success", with many jurisdictions adapting to international standards, they added.
A UK government spokesperson described tacking tax avoidance as a "priority" and said they had been at the "forefront of international action".