15 U.S.C. § 6155
Telephone numbers registered on the national "do-not-call" registry of the Telemarketing Sales Rule (16 CFR 310.4(b)(1)(iii)) since the establishment of the registry and telephone numbers registered on such registry after March 11, 2003, shall not be removed from such registry except as provided for in subsection (b) or upon the request of the individual to whom the telephone number is assigned.
The Federal Trade Commission shall periodically check telephone numbers registered on the national "do-not-call" registry against national or other appropriate databases and shall remove from such registry those telephone numbers that have been disconnected and reassigned. Nothing in this section prohibits the Federal Trade Commission from removing invalid telephone numbers from the registry at any time.
15 U.S.C. § 6155