10 U.S.C. § 774: Religious apparel: wearing while in uniform

(a) General Rule.—Except as provided under subsection (b), a member of the armed forces may wear an item of religious apparel while wearing the uniform of the member’s armed force. (b) Exceptions.—The Secretary concerned may prohibit the wearing of an item of religious apparel—(1) in circumstances with respect to which the Secretary determines that the wearing of the item would interfere with the performance of the member’s military duties; or (2) if the Secretary determines, under regulations under subsection (c), that the item of apparel is not neat and conservative. (c) Regulations.—The Secretary concerned shall prescribe regulations concerning the wearing of religious apparel by members of the armed forces under the Secretary’s jurisdiction while the members are wearing the uniform. Such regulations shall be consistent with subsections (a) and (b). (d) Religious Apparel Defined.—In this section, the term “religious apparel” means apparel the wearing of which is part of the observance of the religious faith practiced by the member.