Md. Code, Bus. Reg. § 9A-502

(a) Except as otherwise provided in this title, a holder of a master, master restricted, or limited heating, ventilation, air–conditioning, and refrigeration license, or other person who engages in the business of providing heating, ventilation, air–conditioning, or refrigeration services, may not employ an individual to provide or assist in providing heating, ventilation, air–conditioning, or refrigeration services unless the individual is licensed by the Board. (b) A person may not employ an individual to provide or assist in providing heating, ventilation, air–conditioning, or refrigeration services under a public work contract subject to Title 17, Subtitle 2 of the State Finance and Procurement Article unless the individual is licensed by the Board. (c) A person may not classify an employee under a public work contract subject to Title 17, Subtitle 2 of the State Finance and Procurement Article who is licensed under this title at a specific work classification that is higher than the employee’s license type.