USA is hardly the type to do bribes. It's a cultural thing mostly, people there feel extremely uncomfortable with them in comparison to the rest of the world (not saying it has never been done before though). Blackmail is also not perhaps the word to use here and it is not usually done much... USA usually goes more along the lines of making a public statement or private statement about them taking measures against them if they don't stop (for some perspectives it might be a form of coercion but from another it is seen as enforcing the law-very convenient lol).
It's NOT enforcing the law.
1. Neither government nor companies enforce the law, courts do. Seperation of powers is an important factor of modern democracies.
2. Wikileaks has not been declared illegal by any court yet.
The first statement of Mastercard about their ban of Wikileaks but not the Ku-Klux Klan side organisation was (not an actual quote, just displaying the content from a German article):
"It might be that some partners are morally questionable, but our rules prohibit working together with illegal organisations or criminals. Thus, as long as the Knights Party (Ku Klux Klan political party) is not legally illegal, Mastercard and Visa do not have a reason of not working with them."
The issue with those points: Not a single court in the world did ever declare Wikileaks to be an illegal organisation nor found them guilty of anything. They are neither illegal nor criminal. Don't forget that the presumption of innocence is one of the very basics of states of law! As long as they aren't found guilty, they're absolutely legal and innocent.
"Meanwhile Mastercard seems to have noticed this as well and distanced from their original statement.
[...]
By now the German press officer of Mastercard has to struggle hard to justify their action without using the word "illegal". According to their new offical version, they only "suspended" their business contacts to Wikileaks "until the situation is clarified." What they actually mean with that, the press officer cannot explain. Visa uses a similar phrasing, speaking of an "inspection of the business relation"."
(by Süddeutsche Zeitung - translated extract from a German article)
"Operation: Payback"
4Chan - I guess most of you will know it, the most freaked out anonymous web forum there is, responsible for all kinds of sudden internet hypes, internet vote manipulation et cetera (afaik Pedobear came from it, they managed to bring "North Korea" up to #1 for Justin Bieber's "where shall the next tour be?" vote and voted "Pedobear" as the offical Miley Cyrus #1 Fan) declared to attack all companies which bow their heads to governments in the Wikileaks affair.
On Tueday the webpage of the suisse "PostFinance" which shutted down a Wikileaks bank account, was offline for some hours due to a "Denial of Service" hacker attack.
On late wednesday morning, the MasterCard webpage went down. 4Chan (or rather their members) is suspected to be the attacker here as well.
(for me it still is down, 16:08 here)
Edit:
Spy, Journalist, High-Tech Terrorist?
The search for the right paragraph: The US courts consider a charge against Julian Assange - Jet they've no idea what to charge him for. Every shady move seems an option for the investigators: They even think about charging him for the injury of copyrights.
Headline of a new article on Sueddeutsche.de
So, even the US courts don't have an idea what possible crime Wikileaks/Assange could've permitted, yet they want to charge him...
This is totally out of control. This is not what a legal state is supposed to do. A state of law is supposed to investigate after a crime has been done and then try to find a fair sentence in a just process. Here no crime has been permitted, but the courts try to punish him nonetheless.
These are not the methods of a democracy and state of law anymore. These are the methods used in the GDR and Soviet Russia: "Oh, he's against us; Let's find
something we can charge him for, it's totally irrelevant what we're punishing him for, but he has to be punished!"