Md. Code Ann., Bus. Reg. § 9A-503
Except as otherwise provided in this title, regardless of whether a person is engaged in the business of providing heating, ventilation, air-conditioning, or refrigeration services, the person may not knowingly employ an individual to provide or assist in providing heating, ventilation, air-conditioning, or refrigeration services in the State unless the individual is licensed by the Board.
Acts 1992, c. 649.