MasterCard and Visa have been threatened with legal action after suspending card payments to WikiLeaks.
DataCell, which facilitates credit card donations to WikiLeaks, has decided to sue both companies in an attempt to make donations through these channels possible again.
"The suspension of payments towards WikiLeaks is a violation of the agreements with their customers," said Andreas Fink, chief executive of DataCell, in a statement.
"They have no problem transferring money for businesses such as gambling sites, pornography services and the like. Why a donation to a web site which is holding up for human rights should be morally any worse is outside of my understanding."
MasterCard previously told V3.co.uk that it would suspend payment to WikiLeaks until the "situation was resolved".
Visa Europe is set to suspend payments for one week beginning 8 December.
"Visa Europe has taken action to temporarily suspend Visa payment acceptance on WikiLeaks' web site pending investigation into whether it contravenes Visa operating rules, including compliance with local laws in the markets where we operate," the firm said in a statement.
MasterCard was the third multinational corporation to have its site taken down by a distributed denial-of-service (DDoS) attack. PayPal and Swiss Bank Post Finance had already been targeted after removing support for WikiLeaks.
"MasterCard is experiencing heavy traffic on its external MasterCard.com corporate web site, but this remains accessible," the company said in a statement to V3.co.uk.
"We are working to restore normal speed of service. There is no impact whatsoever on MasterCard or Maestro cardholders' abilities to use their cards for secure transactions."
However, at the time of publication, MasterCard.com was still not accessible.
Internet activist group Anonymous has taken responsibility for all three attacks in postings to its Twitter page.
The DDoS attacks are different to typical assaults which use botnets comprised of PCs whose owners have downloaded malware unknowingly.
The goal of Anonymous is not to make profit but to cripple and disrupt services to publicise its cause and cause humiliation, according to Noa Bar Yosef, senior security strategist at Imperva.
"Operation Payback is recruiting people from within their own network. They are actually asking supporters to download the piece of code, the DDoS malware itself, that upon wake-up call engages in the DoS," he said.
"There is no victimised machine as the participants knowingly engage in what they call an act of defiance."
The furore around WikiLeaks took another turn this week after founder and editor-in-chief Julian Assange was arrested in the UK on charges of sexual assault and subsequently refused bail.
Assange faces being extradited to Sweden where the attacks are alleged to have taken place.
WikiLeaks, meanwhile, continues to release confidential government cables.
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