28 CFR 540.15 - Restricted general correspondence.
(1) Involvement in any of the activities listed in § 540.14(d);
(2) Attempting to solicit funds or items (e.g., samples), or subscribing to a publication without paying for the subscription;
(3) Being a security risk;
(4) Threatening a government official; or
(5) Having committed an offense involving the mail.
(2) Where there is no incident report, the Warden:
(1) Correspond with the inmate's spouse, mother, father, children, and siblings, unless the correspondent is involved in any violation of correspondence regulations, or would be a threat to the security or good order of the institution;
(2) Request other persons also to be placed on the approved correspondence list, subject to investigation, evaluation, and approval by the Warden; with prior approval, the inmate may write to a proposed correspondence to obtain a release authorizing an investigation; and
(3) Correspond with former business associates, unless it appears to the Warden that the proposed correspondent would be a threat to the security or good order of the institution, or that the resulting correspondence could reasonably be expected to result in criminal activity. Correspondence with former business associates is limited to social matters.
(e) The Warden may allow an inmate additional correspondence with persons other than those on the inmate's approved mailing list when the correspondence is shown to be necessary and does not require an addition to the mailing list because it is not of an ongoing nature.