RE:  US companies are banned from accepting bitcoin as payment

I think that would require statutory action - a new law.  I don't know what authority regulators would have otherwise.

BTW, it seems overreaching to shut down a payment system because someone does something illegal with it.  By that logic, the secret service should go after the U.S. treasury for printing paper bills... because, there's a lot of illegal commerce done using U.S. paper dollars.