Except as provided in subpart B of this part, no work in the industries defined in paragraphs (e) through (k) of § 530.1 shall be done in or about a home, apartment, tenement, or room in a residential establishment unless a special homework certificate issued and in effect pursuant to this part has been obtained for each homeworker or unless the homeworker is so engaged under the supervision of a Sheltered Workshop, as defined in § 525.2 of this chapter.