Numerous payment service providers, including Visa, MasterCard, and PayPal, have blocked donations to WikiLeaks and other legal operations since 2010.

"Banks have been a part of the network of these service providers, which means that the banks actively participate in stopping donations without legitimate grounds," says Pirate Party founder Rick Folkvinge.

The charges have been filed with the Swedish Finansinspektionen, the authority which oversees bank licenses and abuse of position.

"The blockade is a serious threat against the freedoms of opinion and expression", says the Pirate Party's Erik Lönroth, who has been preparing the formal charges. "It must not be up to the individual payment provider to determine which organisations are eligible for donations. At the same time, these charges will bring clarity as to whether the bank regulations of today are sufficient, or if regulations need to be tightened to protect freedom of expression."

WikiLeaks filed a formal complaint with the European Commission in October 2011, claiming that Visa and MasterCard are in breach of EU anti-trust laws.

But late last month the EU governing body signalled that it is unlikely to take action against the card schemes over their refusal to process payments for WikiLeaks after determining that the blockade does not appear to violate anti-trust provisions.