A block on processing donations by credit card companies to WikiLeaks has cost the whistle-blowing website over £30 million, with staff having to take a 40-per-cent pay cut as a result, its founder said today.
Julian Assange described the block as an economic "death penalty" after the European Commission (EC) said it was unlikely to have violated EU anti-trust rules.
The Australian, speaking from Ecuador's embassy in central London, where he has been staying since June to avoid extradition to Sweden to face sexual assault allegations, said the blockade had wiped out 95% of WikiLeaks' revenues.
He claimed that documents obtained by WikiLeaks showed that hard-right politicians in the United States were behind the blockade.
The documents, detailing submissions by Visa and Mastercard to the EC, were heavily redacted, with up to a third of the content blacked out.
He said it was a surprise that the EC was not opening a formal investigation, but pledged that WikiLeaks will continue to fight the blockade.
DataCell, a company that collected donations for WikiLeaks, complained to the Commission about Visa Europe, MasterCard Europe and American Express after they stopped processing donations for WikiLeaks in December 2010.
Their decisions followed criticism by the United States of WikiLeaks' release of thousands of sensitive US diplomatic cables.
Mr Assange, addressing his first press briefing inside the embassy since he took refuge in June, said: "It is concerning that hard-right elements in the United States have been able to pressure Visa and Mastercard into introducing a blockade that the US Treasury has rightly rejected."
Mr Assange said WikiLeaks could be at least 20 times bigger if it was not for the economic blockade.
"It means we have to reduce our publications. We cannot expose war crimes and other forms of abuse.
"We have been living with this banking blockade for two years. The situation is financially difficult, but there is no danger that WikiLeaks will cease as an organisation."
The blockade had wiped out 95% of WikiLeaks' revenues, while its staff, based in countries across the world, have taken a 40% pay cut.
Today's development followed a preliminary decision by the commission, with a final decision expected in the next few weeks.
Mr Assange said the documents published by WikiLeaks today showed that "hard-right" politicians in the United States were directly behind the banking blockade.
Exercising a "financial death penalty" over organisations involved in political controversy set a bad precedent for media and other groups around the world, he said.
"There is no dispute that this blockade is a political reaction to our publications."
Mr Assange added that the EC had been deliberating over the issue for 15 months, almost four times longer than normal.
WikiLeaks and DataCell have now submitted counter arguments to the commission's preliminary decision.
He said he was grateful to the Ecuadorian embassy for "protecting" him and over the granting of political asylum.
"My stay here in the Ecuador Embassy, while difficult in many ways, at least I am able to continue my work to some degree."
He refused to discuss his health or any questions about his stay at the embassy, saying a resolution to his situation was "a matter for diplomacy at this stage".
* The embassy had a fire alarm test after the press briefing, with Mr Assange joking that he did not know where he would go. Police officers remain outside the embassy waiting to arrest Mr Assange if he steps outside.