46 C.F.R. § 10.237
Right of appeal
(a) If the Coast Guard refuses to grant an applicant an MMC, medical certificate, or endorsement it will provide, a written statement listing the reason(s) for denial.
(b) Any person directly affected by a decision or action taken under this subchapter, by or on behalf of the Coast Guard, may appeal under the provisions of subpart 1.03 of part 1 of this chapter.
(c) The Coast Guard will not review decisions made by the Transportation Security Administration to suspend, revoke, or deny a mariner's TWIC.