US regulators don't order ISPs to block websites.
The FBI will occasionally seize a domain, but only after a court order.
Also notice that the FBI has no jurisdiction over foreign domains. It happens that the .com (in addition to .us) registry is in the US, but e.g. the .ru registry is in Russia and not under the jurisdiction of US courts.
Also notice that the FBI has no jurisdiction over foreign domains. It happens that the .com (in addition to .us) registry is in the US, but e.g. the .ru registry is in Russia and not under the jurisdiction of US courts.