Maryland Code, Business Regulation § 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.