Md. Code, Business Regulation § 9A–506

(a) Any subdivision of the State which required a local license to provide heating, ventilation, air-conditioning, or refrigeration services on or before January 1, 1990 may continue to require a local license for services performed within that subdivision.

(b) (1) A subdivision of the State which requires a local license to provide heating, ventilation, air-conditioning, or refrigeration services may not discriminate against applicants who are not residents of the subdivision.

(2) A subdivision of the State which requires a local license to provide heating, ventilation, air-conditioning, or refrigeration services shall issue a local license to any individual licensed by the Board on receipt from the individual of any application and fee required by the subdivision of the State.

(3) A subdivision of the State may not require an applicant for a local license to provide heating, ventilation, air-conditioning, or refrigeration services to take an examination if the applicant is licensed by the Board.

(c) In the event that any subdivision which requires a local license discontinues that requirement after the effective date of this Act, that subdivision may not thereafter adopt a license requirement.

(d) A State license is required to provide heating, ventilation, air-conditioning, or refrigeration services anywhere within the State, whether or not the individual holds a local license.