Md. Code, Business Occupations and Professions § 12–402

(a) A master plumber, holder of a limited master plumber license, or other person who engages in the business of providing plumbing services under this subtitle may employ an individual who is not a master plumber or holder of a limited master plumber license to provide or assist in providing plumbing services if the individual:

(1) is licensed:

(i) as an apprentice plumber, to assist in providing plumbing services; or

(ii) as a journey plumber or holder of a limited journey plumber license, to provide plumbing services; and

(2) provides or assists in providing the services only within the scope of the license.

(b) This section does not apply to an individual performing work that is only incidental to the licensee providing or assisting in providing plumbing services.