I don't think this holds water comrade. Not all communication of information is 'free speech'; transmitting a computer virus, for example, falls outside the definition.
Yikes! I hope that's not the case, especially as online transactions become more and more a part of how businesses and organizations operate.
If the few companies who do online payment processing can decide who can and who can't receive online payments at their own discretion then doesn't that give them a tremendous and inordinate amount of power? Imagine if MC and Visa and Paypal decided they didn't want to process donations to the green party, or to a consumer advocacy group that advocated for more transparency and regulation of the credit card industry, for example.