47 C.F.R. § 64.1512
Nothing in this subpart shall preclude a common carrier or information provider from blocking or ordering the blocking of its interstate pay-per-call programs from numbers assigned to subscribers who have incurred, but not paid, legitimate pay-per-call charges, except that a subscriber who has filed a complaint regarding a particular pay-per-call program pursuant to procedures established by the Federal Trade Commission under title III of the TDDRA shall not be involuntarily blocked from access to that program while such a complaint is pending. This restriction is not intended to preclude involuntary blocking when a carrier or IP has decided in one instance to sustain charges against a subscriber but that subscriber files additional separate complaints.
47 C.F.R. §64.1512